advance cp ii
TRANSCRIPT
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Data communication is the process of communicating information in binary from
between two or more points. Data communication is sometimes called computer
communications because most of the information interchanged today is between
computers, or between computers and their terminals, printers or other peripheral
devices. The data might be as elementary as the binary symbols 1 and 0, or as
complex as the characters represented by the keys on a typewriter keyboard. In this
case, the characters or symbols represent information.
General Data Communication System
The following diagram show the general data communication system, which consist
of following three component.
1. The Transmitter (SOURCE)2. The Receiver (DESTINATION)3. The Transmission Path (Channel)
General Data Communication System
Universal Seven Part Data Circuit
The following diagram show the Universal Seven Part Data Circuit, which consist of
following seven component.
1. DTE at Point A2. DCE at Point A3. DTE at Point B4. DCE at Point B5. DTE-DCE Interface at Point A6. DTE-DCE Interface at Point B7. Communication Channel
Universal Seven Part Data Circuit
SOURCE
SINK
SINK
SOURCE
DTE DTEDCE DCE
Point A Point B
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DTE : Data Terminal Equipment
DCE : Data Carrier Equipment
DTE-DCE Interface : A set of rule which specify the data movement across the
interface between DTE-DCE. It is also called RS-232
Standard or V.24.
Serial and Parallel Data Transmission
If the bits move one by one over a single line it is called SERIAL data transmission.
If a groups of bits move over several lines at the same time it is called PARALLE
data transmission.
Synchronous/Asynchronous Serial Transmission
Synchronous Asynchronous
1. Speed of transmitter and receiver isdifferent. Speed of transmitter and receiveris almost same.
2. Data are send in a GROUP called blocks,
with special synchronization characters
placed at start and end.
Data are send in bit by bit, many
special characters are sent along
with data.
3. Error checking is performed automatically
on entire block. (if any error entire block is
retransmitted)
Manually Error checking is done.
Modes of Communication
Simplex
Data in a simplex channel is always one way. Simplex channels are not oftenused because it is not possible to send back error or control signals to thetransmit end.
It's like a one way street. An example of simplex is Television, or Radio.
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Half Duplex
A half-duplex channel can send and receive, but not at the same time. It's likea one-lane bridge where two way traffic must give way in order to cross. Onlyone end transmits at a time, the other end receives. In addition, it is possibleto perform error detection and request the sender to retransmit information
that arrived corrupted. In some aspects, you can think of Internet surfing asbeing half-duplex, as a user issues a request for a web document, then thatdocument is downloaded and displayed before the user issues anotherrequest.
Another example of half-duplex is talk-back radio, and CB Radio (Citizens
Band). You might have seen movies where truckies (drivers of very big trucks)communicate to each other, and when they want the other person to speakthey say "over". This is because only one person can talk at a time.
Full Duplex
Data can travel in both directions simultaneously. There is no need to switchfrom transmit to receive mode like in half duplex. Its like a two lane bridge ona two-lane highway. Have you ever watched these television talk showswhere the host has a number of people on the show, and they all try to talk atonce. Well, that's full duplex!
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Parallel port is a simple and inexpensive tool for building computer controlled
devices and projects. The simplicity and ease of programming makes parallel port
popular in electronics hobbyist world. The parallel port is often used in Computer
controlled robots, Atmel/PIC programmers, home automation, ...etc... Here a simple
tutorial on parallel port interfacing and programming with some examples.
Everybody knows what is parallel port, where it can be found, and for what itis being used. the primary use of parallel port is to connect printers to computer and is
specifically designed for this purpose. Thus it is often called as printer Port or
Centronics port (this name came from a popular printer manufacturing company
'Centronics' who devised some standards for parallel port). You can see the parallel
port connector in the rear panel of your PC. On almost all the PCs only one parallel
port is present, but you can add more by buying and inserting ISA/PCI parallel port
cards. The port is composed of 4 control lines, 5 status lines and 8 data lines. It's
found commonly on the back of your PC as a D-Type 25 Pin female connector. There
may also be a D-Type 25 pin male connector.
Parallel port modes
The IEEE 1284 Standard which has been published in 1994 defines five modes
of data transfer for parallel port. They are,
1) Compatibility Mode
2) Nibble Mode
3) Byte Mode
4) EPP
5) ECP
The aim was to design new drivers and devices which were compatible with each
other and also backwards compatible with the Standard Parallel Port (SPP).
Compatibility, Nibble & Byte modes use just the standard hardware available on the
original Parallel Port cards while EPP & ECP modes require additional hardware
which can run at faster speeds, while still being downwards compatible with the
Standard Parallel Port.
Compatibility mode or "Centronics Mode" as it is commonly known, can only send
data in the forward direction at a typical speed of 50 kbytes per second but can be as
high as 150+ kbytes a second. In order to receive data, you must change the mode to
either Nibble or Byte mode. Nibble mode can input a nibble (4 bits) in the reverse
direction. E.g. from device to computer. Byte mode uses the Parallel's bi-directional
feature (found only on some cards) to input a byte (8 bits) of data in the reverse
direction.
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Hardware
The pin outs of DB25 connector is shown in the picture below
Pin No(DB25)
Signal name Direction Register -bit
Inverted
1 nStrobe Out Control-0 Yes
2 Data0 In/Out Data-0 No
3 Data1 In/Out Data-1 No
4 Data2 In/Out Data-2 No
5 Data3 In/Out Data-3 No
6 Data4 In/Out Data-4 No
7 Data5 In/Out Data-5 No
8 Data6 In/Out Data-6 No
9 Data7 In/Out Data-7 No
10 nAck In Status-6 No11 Busy In Status-7 Yes
12 Paper-Out In Status-5 No
13 Select In Status-4 No
14 Linefeed Out Control-1 Yes
15 nError In Status-3 No
16 nInitialize Out Control-2 No
17 nSelect-Printer Out Control-3 Yes
18-25 Ground - - -
LPT1(Parallel Port) is normally assigned base address 378h, while LPT2 is assigned
278h. However this may not always be the case as explained later. 378h & 278h have
always been commonly used for Parallel Ports. The lower case h denotes that it is in
hexadecimal. These addresses may change from machine to machine.
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Address Notes:3BCh - 3BFh Used for Parallel Ports which were
incorporated on to Video Cards - Doesn'tsupport ECP addresses
378h - 37Fh Usual Address For LPT 1278h - 27Fh Usual Address For LPT 2
Port Addresses
When the computer is first turned on, BIOS (Basic Input/Output System) will
determine the number of ports you have and assign device labels LPT1, LPT2 &
LPT3 to them. BIOS first looks at address 3BCh. If a Parallel Port is found here, it is
assigned as LPT1, then it searches at location 378h. If a Parallel card is found there, it
is assigned the next free device label. This would be LPT1 if a card wasn't found at
3BCh or LPT2 if a card was found at 3BCh. The last port of call, is 278h and follows
the same procedure than the other two ports. Therefore it is possible to have a LPT2
which is at 378h and not at the expected address 278h.
What can make this even confusing, is that some manufacturers of Parallel Port
Cards, have jumpers which allow you to set your Port to LPT1, LPT2, LPT3. Now
what address is LPT1? - On the majority of cards LPT1 is 378h, and LPT2, 278h, but
some will use 3BCh as LPT1, 378h as LPT1 and 278h as LPT2.Life wasn't meant to
be easy.
The lines in DB25 connector are divided in to three groups, they are
1) Data lines (data bus)
2) Control lines
3) Status lines
As the name refers , data is transferred over data lines , Control lines are used
to control the peripheral and of course , the peripheral returns status signals back
computer through Status lines. These lines are connected to Data, Control And Status
registers internally . The details of parallel port signal lines are given below.
Parallel port registers
As you know, the Data, Control and status lines are connected to there
corresponding registers inside the computer. So by manipulating these registers in
program , one can easily read or write to parallel port with programming languages
like 'C' and BASIC.
The registers found in standard parallel port are ,
1) data register
2) Status register
3) Control register
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As there names specifies, Data register is connected to Data lines, Control register is
connected to controll lines and Status lregistyer is connected to Status lines. (Here the
word connection does not mean that there is some physical connection between
data/control/status lines. The registers are virtually connected to the corresponding
lines.). So what ever you write to these registers , will appear in corresponding lines
as voltages, Of course, you can measure it with a multimeter. And What ever you give
to Parallel port as voltages can be read from these registers(with some restrictions).For example , if we write '1' to Data register , the line Data0 will be driven to +5v.
Just like this ,we can programmatically turn on and off any of the data lines and
Control lines.
Where these registers are ?
In an IBM PC, these registers are IO mapped and will have unique address. We
have to find these addresses to to work with parallel port. For a typical PC , the base
address of LPT1 is 0x378 and of LPT2 is 0x278. The data register resides at this base
address , status register at baseaddress + 1 and the control register is at baseaddress +
2. So once we have the base address , we can calculate the address of each registers in
this manner. The table below shows the register addresses of LPT1 and LPT2.
Register LPT1 LPT2
data registar(baseaddress + 0) 0x378 0x278
status register (baseaddress + 1) 0x379 0x279
control register (baseaddress + 2) 0x37a 0x27a
Software Registers - Standard Parallel Port (SPP)
Offset Name Read/Write Bit No. Properties
Bit 7 Data 7Bit 6 Data 6Bit 5 Data 5Bit 4 Data 4Bit 3 Data 3Bit 2 Data 2Bit 1 Data 1
Base + 0 DataPort
Write(Note-1)
Bit 0 Data 0Data Port
Note 1 : If the Port is Bi-Directional then Read and Write Operations can be
performed on the Data Register.
The base address, usually called the Data Port or Data Register is simply used for
outputting data on the Parallel Port's data lines (Pins 2-9). This register is normally a
write only port. If you read from the port, you should get the last byte sent. However
if your port is bi-directional, you can receive data on this address. See Bi-directional
Ports for more detail.
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Offset Name Read/Write Bit No. PropertiesBit 7 BusyBit 6 AckBit 5 Paper OutBit 4 Select InBit 3 Error
Bit 2 IRQ (Not)Bit 1 Reserved
Base+ 1
StatusPort
Read Only
Bit 0 ReservedStatus Port
The Status Port (base address + 1) is a read only port. Any data written to this port
will be ignored. The Status Port is made up of 5 input lines (Pins 10,11,12,13 & 15), a
IRQ status register and two reserved bits. Please note that Bit 7 (Busy) is a active low
input. E.g. If bit 7 happens to show a logic 0, this means that there is +5v at pin 11.
Likewise with Bit 2. (nIRQ) If this bit shows a '1' then an interrupt has not occurred.
Offset Name Read/Write Bit No. PropertiesBit 7 UnusedBit 6 UnusedBit 5 Enable Bi-
Directional PortBit 4 Enable IRQ Via
Ack LineBit 3 Select PrinterBit 2 Initialize Printer
(Reset)Bit 1 Auto Linefeed
Base + 2 ControlPort
Read/Write
Bit 0 Strobe
Control PortPORT ACCESS
The C language can be used to transfer data to and from the contents of the various
registers and controllers associated with the IBM-PC. These registers and control
devices are port mapped, and are accessed using special IN and OUT instructions.
Most C language support library's include functions to do this. The following is a
brief description of how this may be done.
#include outp( Port_Address, value); /* turboC uses outportb() */
value = inp( Port_address); /* and inportb() */
Example :outp (0x378,10); /*send the decimal value (10) to the port
(0x378)(lpt1)(Parallel Port)*/
value = inp(0x378); /*recive the value from the port(0x378)(lpt1)(Parallel Port)*/
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The various devices, and their port values, are shown below,
Port Range Device
00 - 0f DMA Chip 8737
20 - 21 8259 PIC
40 - 43 Timer Chip 825360 - 63 PPI 8255 (cassette, sound)
80 - 83 DMA Page registers
200 - 20f Game I/O Adapter
278 - 27f Reserved
2f8 - 2ff COM2
378 - 37f Parallel Printer
3b0 - 3bf Monochrome Display
3d0 - 3df Color Display
3f0 - 3f7 Diskette
3f8 - 3ff COM1
Example of Interfacing Parallel Port :
1. Demonstration of control of light Bulb through parallelport :
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The Software Controlling the above Circuit :1. C program to control ON/OFF Through keyboard
#include
void main(void)
{
outportb(0x378,0x01); //turn on the bulb
getch(); //wait for any key to be pressed
outportb(0x378,0x00); //turn off the bulb
getch(); // wait for a key to be Pressed
}
2. C program to have the bulb blink for five times
for (int i=1; i
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What happens, when you press a key on the keyboard while processor is busy doing
some other work .No matter what the processor is doing, we'll see a letter,
corresponding to the key pressed, displayed on the screen. Since pressing a key
interrupts the processor, we say that keyboard interrupt is generated.
So in simple terms, interrupt is a signal that causes the processor to stop what it is
doing and initiates the processor to take up another job. Once the newly taken job iscompleted, it resumes doing what it was doing before the interrupt occurred. This
resumption is possible because, whenever an interrupt occurs, the processor saves it's
current state by pushing all it's internal registers(CPU's internal memory) onto the
stack (data structure that stores elements in last-in-first-out "LIFO" manner) and pops
out the registers when it is ready for resumption.
There are two types of interrupts (i) software interrupts (generated by program) also
called as trap or exception (256), (ii) Hardware interrupts (generated by
hardware)(15). Every interrupt has it's own interrupt handler. An interrupt handler is a
program that resides some where in the memory. So when an interrupt occurs
processor executes the corresponding interrupt handler. Addresses of these interrupt
handlers are stored in a table known as IVT(Interrupt Vector Table).When aninterrupt occurs, processor obtains the address of the interrupt handler from the IVT
and executes the handler. Every interrupt is assigned a number, interrupt-9h for
keyboard,interrupt-8h for timer and so on. When invoking an interrupt we also need
to pass some parameters, which are simply numbers. These parameters are passed in
CPU registers and known as sub-functions.
Why do we need these subfunctions? For example, lets take interrupt-10h,which
deals with screen. This interrupt allows us to switch between text and graphic
modes(sub-functions 41h and 42h),allows to write a character to the screen(sub-
function Ah),allows us to clear the screen(sub-function 42h) and so on. So we pass
sub-functions to tell which specific functionality of the interrupt we want to use.
THE INT86() FUNCTION
This function is general 8086 software interrupt interface used to make a software
interrupt occur and then invoke ROM-BIOS function. Here int stands for interrupt
and 86 represnts 8086 family of processor.
Int int86(int into_no, union REGS *inregs, union REGS *outregs);
prototype in dos.h
executes 8086 software interrupt specified by intr_num
copies register values from inregs into the registers
after the software interrupt execution it returns register values into the outregs.
Status of the carry flag into x.cflag in outregs
Value of the 8086 flags register into the x.flags field in outregs.
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Example :
(1) Following program display the HELLO at 34,54 position using int86() function.
#include
Void main(){
clrscr();
function(34,54);
printf(HELLO);
}
void function (int x, int y)
{
union REGS regs;
regs.ah=2; /*sets cursor position */
regs.h.dh = y;
regs.h.dl = x;
regs.h.bh = 0; /*video page*/
int86(VIDEO,®s,®s);
}
(2) Following program returns the number of 1kbyet memory blocks present in the
system. The value is return in AX register.
#include
void main()
{
biosmemory();}
int biosmemory()
{
union REGS regs;
int86(0x12,®s,®s);
return(regs.x.ax);
}
KEY BOARD BIOS CALLInt 16H interrupt in the ROM BIOS provides for inimal character transfer
from the keyboards. To perform desired task we have to set the value in AH register.
AH = 0 Get Key
Returns AH = Scan Code
AL = Ascii char, 0 = non-ascii, (ie Function Keys)
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AH = 2 Get Shift Status
Returns
AL = 7 right shift pressed
AL = 6 Left shift pressed
AL = 5 ctrl
AL = 4 altr
AL = 3 scroll lock 1 = onAL = 2 num lock
AL = 1 caps lock
AL = 0 Ins
int int86x( int intr_num, union REGS *inregs, union REGS *outregs,
struct SREGS *segregs )
prototype in dos.h
Executes 8086 software interrupt specified by intr_num
Copies register values from inregs into the registers also copies segregs->x.ds and segregs->y.es into DS/ES
FOLLOWING INTERRUPT EXECUTE DOS INTERRUPT 0x21
int intdos(union REGS *inregs, union REGS *outregs )
prototype in dos.h
Executes 8086 software interrupt INT 21 (DOS INTERRUPT)
Copies register values from inregs into the registers
unique to DOS
int intdosx(union REGS *inregs, union REGS *outregs,
struct SREGS *segres )
prototype in dos.h
Executes 8086 software interrupt INT 21 (DOS INTERRUPT)
Copies register values from inregs into the registers also copies segregs->x.ds and segregs->y.es into DS/ES
There are many ways to interact with hardware.
1. Using high level language functions.2. Using ROM-BIOS Function.3. Using DOS function stored in IO.SYS and MSDOS.SYS4. Direct programming the hardware.
As programmer moves from fist to last approach his reliability decreases and speed
increases.
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ROM BIOS CALLS
The ROM BIOS (Basic Input Output System) provides device control for the PC's
major devices (disk, video, keyboard, serial port, printer), allowing a programmer to
communicate with these devices without needing detailed knowledge of their
operation. The ROM routines are accessed via the Intel 8088/86 software generated
interrupts. The interrupts 10H through to 1AH each access a different routine.
There are mainly three operation performed by BIOS are
Keyboard routine
Video routine
Printer routines
The start-up routine
Routines are responsible for the POST, the process by which the computer test
for the minimum hardware requirements. Second task is to initialized memory and
create equipment list as well as Interrupt Vector Table. Then rest of the boot-upprocess goes on. Lastly the start-up routine load into memory the first of several
bootstrap loader routines into memory.
The ROM Basic Routine
It is not much used now a days, but used for imbedded routines which were
designed to support the early BASIC programming language. These routines were
used to boot computer without an operating system installed.
The ROM Extensions routines
These types of routines provides support for new hardware.
How to use ROM-BIOS Function
Parameters are passed to and from the BIOS routines using the 8088/86 CPU
registers. The routines normally preserve all registers except AX and the flags. Some
registers are altered if they return values to the calling process.
ROM BIOS INTERRUPT ROUTINES
10 Video routines
11 Equipment Check
12 Memory Size Determination
13 Diskette routines
14 Communications routines15 Cassette
16 Keyboard routines
17 Printer
18 Cassette BASIC
19 Bootstrap loader
1A Time of Day
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The interrupts which handle devices are like a gateway which provide access to more
than one routine. The routine executed will depend upon the contents of a particular
CPU register. Each of the software interrupt calls use the 8088/86 register contents to
determine the desired function calls. It is necessary to use a C definition of the CPU
programming model; this allows the registers to be initialized with the correct values
before the interrupt is generated. The definition also provides a convenient place to
store the returned register values. Luckily, the definition has already been created, andresides in the header file dos.h. It is a union of type REGS, which has two parts, each
structures.
One structure contains the eight bit registers (accessed by .h.), whilst the other
structure contains the 16 bit registers (accessed by .x.) To generate the desired
interrupt, a special function call has been provided. This function accepts the interrupt
number, and pointers to the programming model union for the entry and return
register values.
General Purpose RegisterUnioun REGS
{Struct WORDREGS x;
Struct BYTEREGS h;
};
WORDREGS and BYTEREGS structure stores the following registers.
Struct BYTEREGS
{
Unsigned char al,ah,bl,bh;
Unsigned char cl,ch,dl,dh;
};
Struct WORDREGS
{
Unsigned char ax,bx,cx,dx;
Unsigned char si,di,cflag,flaghs;
};
Segment Register
Struct SREGS
{
unsigned int es;unsigned int cs;
unsigned int ss;
unsigned int ds;
}
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There are total 16 registers in the 8086 Microprocessor.
First 4 Registers :
It is also known as DATA registers. Because these registers are used for datamanipulation.
They are ax, bx, cx & dx.
All registers are 16-bit long.
All registers are divided into two part (i.e High Order bit and Low Order bit).
16-bit
Register8-bit Register8-bit Register
ax ah Al
bx bh Bl
cx ch Cl
dx dh dl
Each 16-bit registers either can be used for a whole register (i.e all 16-bit) orcan be used as two register (i.e two 8-bit).
We can't used one 16-bit register and two 8-bit registers at a time.
Ex:- if we are using ax as 16-bit register then we can't used ah or al.
Second 4 Registers :
It is also know as Index / Pointer registers.
They are sp, bp, si & di.
Index and Pointer registers are used for the arithmetic operation in 8086
architecture.
Another 2 Registers :
(i) Instruction Pointer (ip):
It has important instruction that which instruction is executed by our CPU.
IP/Program Counter is used to store the memory location of the next
instruction to be executed.
CPU will check each time the program counter and then it will execute the
next instruction.
On each instruction it will update the program counter.
(ii) Status Register (Flags):
9-bits of status registers are used as control flags(3) and status(6).
Control Flags are used to control come mode of CPU.
Status Flags gives the status of any operation performed by CPU.
There is only one value possible either 0 or 1.
If 1 is there, we can say flag is set.
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Status Flag stores info of the arithmetic & logical instruction.
Ex.: Zero Flag is set to 1 when the result of any arithmetic operation is zero.
Total Flag Registers are shown below.
O D I T S Z A P C
In above figure red flags are not used. Other flags (registers) are explain
below.
O - OverFlow S - SignD - Direction Z - ZeroI - Interrupt A - AuxiliaryT - Trip P Parity
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The Serial Port is harder to interface than the Parallel Port. In most cases, any device
you connect to the serial port will need the serial transmission converted back to
parallel so that it can be used. This can be done using a UART. On the software side
of things, there are many more registers that you have to attend to than on a Standard
Parallel Port. (SPP)
So what are the advantages of using serial data transfer rather than parallel?
1. Serial Cables can be longer than Parallel cables. The serial port transmits a '1' as -
3 to -25 volts and a '0' as +3 to +25 volts where as a parallel port transmits a '0' as
0v and a '1' as 5v. Therefore the serial port can have a maximum swing of 50V
compared to the parallel port which has a maximum swing of 5 Volts. Therefore
cable loss is not going to be as much of a problem for serial cables than they are
for parallel.
2. You don't need as many wires than parallel transmission. If your device needs to
be mounted a far distance away from the computer then 3 core cable (Null
Modem Configuration) is going to be a lot cheaper that running 19 or 25 core
cable. However you must take into account the cost of the interfacing at each end.
3. Infra Red devices have proven quite popular recently. You may of seen manyelectronic diaries and palmtop computers which have infra red capabilities build
in. However could you imagine transmitting 8 bits of data at the one time across
the room and being able to (from the devices point of view) decipher which bits
are which? Therefore serial transmission is used where one bit is sent at a time.
IrDA-1 (The first infra red specifications) was capable of 115.2k baud and was
interfaced into a UART. The pulse length however was cut down to 3/16th of a
RS232 bit length to conserve power considering these devices are mainly used on
diaries, laptops and palmtops.
4. Microcontroller's have also proven to be quite popular recently. Many of these
have in built SCI (Serial Communications Interfaces) which can be used to talk to
the outside world. Serial Communication reduces the pin count of these MPU's.Only two pins are commonly used, Transmit Data (TXD) and Receive Data
(RXD) compared with at least 8 pins if you use a 8 bit Parallel method (You may
also require a Strobe).
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Hardware :
Hardware Properties
Devices which use serial cables for their communication are split into two categories.
These are DCE (Data Communications Equipment) and DTE (Data Terminal
Equipment.) Data Communications Equipment are devices such as your modem, TAadapter, plotter etc while Data Terminal Equipment is your Computer or Terminal.
The electrical specifications of the serial port is contained in the EIA (Electronics
Industry Association) RS232C standard. It states many parameters such as
1. A "Space" (logic 0) will be between +3 and +25 Volts.2. A "Mark" (Logic 1) will be between -3 and -25 Volts.3. The region between +3 and -3 volts is undefined.4. An open circuit voltage should never exceed 25 volts. (In
Reference to GND)5. A short circuit current should not exceed 500mA. Thedriver should be able to handle this without damage.(Take note of this one!)
Above is no where near a complete list of the EIA standard. Line Capacitance,
Maximum Baud Rates etc are also included. For more information please consult the
EIA RS232-C standard. It is interesting to note however, that the RS232C standard
specifies a maximum baud rate of 20,000 BPS!, which is rather slow by today's
standards. A new standard, RS-232D has been recently released.
Serial Ports come in two "sizes", There are the D-Type 25 pin connector and the D-
Type 9 pin connector both of which are male on the back of the PC, thus you willrequire a female connector on your device. Below is a table of pin connections for the
9 pin and 25 pin D-Type connectors.
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Serial Pinouts (D25 and D9 Connectors)
D-Type-25Pin No.
D-Type-9Pin No.
Abbreviation Full Name
Pin 2 Pin 3 TD Transmit DataPin 3 Pin 2 RD Receive DataPin 4 Pin 7 RTS Request To
SendPin 5 Pin 8 CTS Clear To SendPin 6 Pin 6 DSR Data Set ReadyPin 7 Pin 5 SG Signal GroundPin 8 Pin 1 CD Carrier DetectPin 20 Pin 4 DTR Data Terminal
ReadyPin 22 Pin 9 RI Ring Indicator
Table : D Type 9 Pin and D Type 25 Pin Connectors
Pin Functions
Abbreviation Full Name Function
TD Transmit Data Serial Data Output (TXD)RD Receive Data Serial Data Input (RXD)CTS Clear to Send This line indicates that the Modem is ready to
exchange data.DCD Data Carrier
DetectWhen the modem detects a "Carrier" fromthe modem at the other end of the phoneline, this Line becomes active.
DSR Data SetReady
This tells the UART that the modem is readyto establish a link.
DTR Data TerminalReady
This is the opposite to DSR. This tells theModem that the UART is ready to link.
RTS Request ToSend
This line informs the Modem that the UARTis ready to exchange data.
RI Ring Indicator Goes active when modem detects a ringingsignal from the PSTN.
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Serial Port's Registers :
Port Addresses & IRQ's
Name Address IRQCOM 1 3F8 4COM 2 2F8 3COM 3 3E8 4COM 4 2E8 3
Table : Standard Port Addresses
Above is the standard port addresses. These should work for most P.C's. If you just
happen to be lucky enough to own a IBM P/S2 which has a micro-channel bus, then
expect a different set of addresses and IRQ's. Just like the LPT ports, the base
addresses for the COM ports can be read from the BIOS Data Area.
Null Modems
A Null Modem is used to connect two DTE's together. This is commonly used as a
cheap way to network games or to transfer files between computers using Zmodem
Protocol, Xmodem Protocol etc. This can also be used with many Microprocessor
Development Systems.
Figure : Null Modem Wiring Diagram
Above is my preferred method of wiring a Null Modem. It only requires 3 wires (TD,
RD & SG) to be wired straight through thus is more cost effective to use with long
cable runs. The theory of operation is reasonably easy. The aim is to make to
computer think it is talking to a modem rather than another computer. Any data
transmitted from the first computer must be received by the second thus TD is
connected to RD. The second computer must have the same set-up thus RD is
connected to TD. Signal Ground (SG) must also be connected so both grounds are
common to each computer.
The Data Terminal Ready is looped back to Data Set Ready and Carrier Detect on
both computers. When the Data Terminal Ready is asserted active, then the Data Set
Ready and Carrier Detect immediately become active. At this point the computer
thinks the Virtual Modem to which it is connected is ready and has detected the
carrier of the other modem.
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All left to worry about now is the Request to Send and Clear To Send. As both
computers communicate together at the same speed, flow control is not needed thus
these two lines are also linked together on each computer. When the computer wishes
to send data, it asserts the Request to Send high and as it's hooked together with the
Clear to Send, It immediately gets a reply that it is ok to send and does so.
Notice that the ring indicator is not connected to anything of each end. This line isonly used to tell the computer that there is a ringing signal on the phone line. As we
don't have a modem connected to the phone line this is left disconnected.
DTE / DCE SpeedsWe have already talked briefly about DTE & DCE. A typical Data Terminal Device is
a computer and a typical Data Communications Device is a Modem. Often people will
talk about DTE to DCE or DCE to DCE speeds. DTE to DCE is the speed between
your modem and computer, sometimes referred to as your terminal speed. This should
run at faster speeds than the DCE to DCE speed. DCE to DCE is the link between
modems, sometimes called the line speed.
Most people today will have 28.8K or 33.6K modems. Therefore we should expect
the DCE to DCE speed to be either 28.8K or 33.6K. Considering the high speed of the
modem we should expect the DTE to DCE speed to be about 115,200
BPS.(Maximum Speed of the 16550a UART) This is where some people often fall
into a trap. The communications program which they use have settings for DCE to
DTE speeds. However they see 9.6 KBPS, 14.4 KBPS etc and think it is your modem
speed.
Today's Modems should have Data Compression build into them. This is very much
like PK-ZIP but the software in your modem compresses and decompresses the data.
When set up correctly you can expect compression ratios of 1:4 or even higher. 1 to 4
compression would be typical of a text file. If we were transferring that text file at28.8K (DCE-DCE), then when the modem compresses it you are actually transferring
115.2 KBPS between computers and thus have a DCE-DTE speed of 115.2 KBPS.
Thus this is why the DCE-DTE should be much higher than your modem's connection
speed.
Some modem manufacturers quote a maximum compression ratio as 1:8. Lets say for
example its on a new 33.6 KBPS modem then we may get a maximum 268,800 BPS
transfer between modem and UART. If you only have a 16550a which can do 115,200
BPS tops, then you would be missing out on a extra bit of performance. Buying a
16C650 should fix your problem with a maximum transfer rate of 230,400 BPS.
However don't abuse your modem if you don't get these rates. These are MAXIMUM
compression ratios. In some instances if you try to send a already compressed file,your modem can spend more time trying the compress it, thus you get a transmission
speed less than your modem's connection speed. If this occurs try turning off your
data compression. This should be fixed on newer modems. Some files compress easier
than others thus any file which compresses easier is naturally going to have a higher
compression ratio.
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Flow Control
So if our DTE to DCE speed is several times faster than our DCE to DCE speed the
PC can send data to your modem at 115,200 BPS. Sooner or later data is going to get
lost as buffers overflow, thus flow control is used. Flow control has two basic
varieties, Hardware or Software.
Software flow control, sometimes expressed as Xon/Xoff uses two characters Xon
and Xoff. Xon is normally indicated by the ASCII 17 character where as the ASCII 19
character is used for Xoff. The modem will only have a small buffer so when the
computer fills it up the modem sends a Xoff character to tell the computer to stop
sending data. Once the modem has room for more data it then sends a Xon character
and the computer sends more data. This type of flow control has the advantage that it
doesn't require any more wires as the characters are sent via the TD/RD lines.
However on slow links each character requires 10 bits which can slow
communications down.
Hardware flow control is also known as RTS/CTS flow control. It uses two wires in
your serial cable rather than extra characters transmitted in your data lines. Thus
hardware flow control will not slow down transmission times like Xon-Xoff does.
When the computer wishes to send data it takes active the Request to Send line. If the
modem has room for this data, then the modem will reply by taking active the Clear to
Send line and the computer starts sending data. If the modem does not have the room
then it will not send a Clear to Send.
The UART (8250 and Compatibles)
UART stands for Universal Asynchronous Receiver / Transmitter. Its the littlebox of tricks found on your serial card which plays the little games with your
modem or other connected devices. Most cards will have the UART'sintegrated into other chips which may also control your parallel port, gamesport, floppy or hard disk drives and are typically surface mount devices. The8250 series, which includes the 16450, 16550, 16650, & 16750 UARTS arethe most commonly found type in your PC. Later we will look at other typeswhich can be used in your homemade devices and projects.
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Figure : Pin Diagrams for 16550, 16450 & 8250 UARTs
The 16550 is chip compatible with the 8250 & 16450. The only two differences are
pins 24 & 29. On the 8250 Pin 24 was chip select out which functioned only as a
indicator to if the chip was active or not. Pin 29 was not connected on the 8250/16450
UARTs. The 16550 introduced two new pins in their place. These are Transmit Ready
and Receive Ready which can be implemented with DMA (Direct Memory Access).
These Pins have two different modes of operation. Mode 0 supports single transfer
DMA where as Mode 1 supports Multi-transfer DMA.
Mode 0 is also called the 16450 mode. This mode is selected when the FIFO buffers
are disabled via Bit 0 of the FIFO Control Register or When the FIFO buffers are
enabled but DMA Mode Select = 0. (Bit 3 of FCR) In this mode RXRDY is activelow when at least one character (Byte) is present in the Receiver Buffer. RXRDY will
go inactive high when no more characters are left in the Receiver Buffer. TXRDY
will be active low when there are no characters in the Transmit Buffer. It will go
inactive high after the first character / byte is loaded into the Transmit Buffer.
Mode 1 is when the FIFO buffers are active and the DMA Mode Select = 1. In Mode
1, RXRDY will go active low when the trigger level is reached or when 16550 Time
Out occurs and will return to inactive state when no more characters are left in the
FIFO. TXRDY will be active when no characters are present in the Transmit Buffer
and will go inactive when the FIFO Transmit Buffer is completely Full.
All the UARTs pins are TTL compatible. That includes TD, RD, RI, DCD, DSR,
CTS, DTR and RTS which all interface into your serial plug, typically a D-typeconnector. Therefore RS232 Level Converters (which we talk about in detail later) are
used. These are commonly the DS1489 Receiver and the DS1488 as the PC has +12
and -12 volt rails which can be used by these devices. The RS232 Converters will
convert the TTL signal into RS232 Logic Levels.
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Pin No. Name NotesPin 1:8 D0:D7 Data BusPin 9 RCLK Receiver Clock Input. The frequency of
this input should equal the receiversbaud rate * 16
Pin 10 RD Receive Data
Pin 11 TD Transmit DataPin 12 CS0 Chip Select 0 - Active HighPin 13 CS1 Chip Select 1 - Active HighPin 14 nCS2 Chip Select 2 - Active LowPin 15 nBAUDOUT Baud Output - Output from
Programmable Baud Rate Generator.Frequency = (Baud Rate x 16)
Pin 16 XIN External Crystal Input - Used for BaudRate Generator Oscillator
Pin 17 XOUT External Crystal OutputPin 18 nWR Write Line - Inverted
Pin 19 WR Write Line - Not InvertedPin 20 VSS Connected to Common GroundPin 21 RD Read Line - InvertedPin 22 nRD Read Line - Not InvertedPin 23 DDIS Driver Disable. This pin goes low when
CPU is reading from UART. Can beconnected to Bus Transceiver in case ofhigh capacity data bus.
Pin 24 nTXRDY Transmit ReadyPin 25 nADS Address Strobe. Used if signals are not
stable during read or write cyclePin 26 A2 Address Bit 2
Pin 27 A1 Address Bit 1Pin 28 A0 Address Bit 0Pin 29 nRXRDY Receive ReadyPin 30 INTR Interrupt OutputPin 31 nOUT2 User Output 2Pin 32 nRTS Request to SendPin 33 nDTR Data Terminal ReadyPin 34 nOUT1 User Output 1Pin 35 MR Master ResetPin 36 nCTS Clear To SendPin 37 nDSR Data Set Ready
Pin 38 nDCD Data Carrier DetectPin 39 nRI Ring IndicatorPin 40 VDD + 5 Volts
Table : Pin Assignments for 16550A UART
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Programming with Serial Port
Bioscom() is the standard library function declared in the bios.h file.
Declaration: int bioscom(int cmd, char abyte, int port);
Remarks:
bioscom use BIOS interrupt 0x14 to perform various RS-232 communications over
the I/O port given in port.
Argument What It Is/Does
Cmd Specifies the I/O operation to perform
Abyte OR combination of bits that specifies COM port settings (ignored
if cmd = 2 or 3)
Port Identifies the I/O port; 0 = COM1, 1 = COM2, etc.
cmd can be one of the following (defined in BIOS.H):
0 Sets the communications parameters to the value in abyte
1 Sends the character in abyte out over the communications line
2 Receives a character from the communications line
3 Returns current status of the communications port
When cmd = 2 or 3 (_COM_RECEIVE or _COM_STATUS), the abyte argument is
ignored.
When cmd = 0 (_COM_INIT), abyte is an OR combination of the following bits (onefrom each group):
Bioscom Meaning
0x02
0x03
7 data bits
8 data bits
0x00
0x04
1 stop bit
2 stop bits
0x00
0x08
0x18
No parity
Odd parity
Even parity
0x00
0x200x40
0x60
0x80
0xA0
0xC0
0xE0
110 baud
150 baud300 baud
600 baud
1200 baud
2400 baud
4800 baud
9600 baud
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For example:abyte = 0xEB = (0xE0 | 0x08 | 0x00 | 0x03) =
(_COM_9600 | _COM_ODDPARITY | _COM_STOP1 | _COM_CHR8)
The communications port is set to9600 baud (0xE0 = _COM_9600)
Odd parity (0x08 = _COM_ODDPARITY)1 stop bit (0x00 = _COM_STOP1)8 data bits (0x03 = _COM_CHR8)
Return Value:
For all values of cmd, both functions return a 16-bit integer.
The upper 8 bits of the return value are status bits.
If one or more status bits is set to 1, an error has occured.
If no status bits are set to 1, the byte was received without error.
The lower 8 bits of the return value depend on the value of cmd specified:
Value of cmd Lower 8 bits of return value
0 (_COM_INIT) or
3 (_COM_STATUS)
The lower bits are defined as shown below.
1 (_COM_SEND) The byte send to the port.
2 (_COM_RECEIVE) The byte read is in the lower bits of the
return value--if there is no error
(no upper bits are set to 1).
Upper 8 bits of the bioscom return value
15 Time out (set to 1 if abyte value could not be sent)14 Transmit shift register empty
13 Transmit holding register empty
12 Break detect
11 Framing error
10 Parity error
9 Overrun error
8 Data ready
Lower 8 bits (these vary, depending on the value of cmd)0 Received line signal detect
1 Ring indicator
2 Data set ready
3 Clear to send
4 Change in receive line signal detector
5 Trailing edge ring detector
6 Change in data set ready
7 Change in clear to send
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Example
Our program will display whatever is typed on one computer on the other computer.
The two machines are connected through the serial cable & both running the same
program.
#include #include
#include #define COM1 0
#define DATA_READY 0x100
#define TRUE 1#define FALSE 0#define SETTINGS ( 0x80 | 0x02 | 0x00 | 0x00)
int main(void)
{int in, out, status, DONE = FALSE;
bioscom(0, SETTINGS, COM1);
printf("... BIOSCOM [ESC] to exit ...\n");
while (!DONE)
{ status = bioscom(3, 0, COM1);if (status & DATA_READY)
if ((out = bioscom(2, 0, COM1) & 0x7F) != 0)putch(out);
if (kbhit())
{ if ((in = getch()) == '\x1B')DONE = TRUE;bioscom(1, in, COM1);
}}
return 0;}
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Interrupt No. and Service No.
Interrupt Service How to Use
33h 0
Reset mouse and get status
Call with:
AX = 0000h
Returns:AX = FFFFh (If mouse support is available)AX = 0000h (If mouse support is not available)
33h 1
Show mouse pointer
Call with:AX = 0001h
Returns:Nothing
33h 2
Hide mouse pointer
Call with:AX = 0002h
Returns:Nothing
33h 3
Get mouse position and button status
Call with:AX = 0003h
Returns:BX = mouse button status
Bit Significance
0 left button is down1 right button is down2 center button is downCX = x coordinateDX = y coordinate
33h 4
Set mouse pointer position
Call with:AX = 0004hCX = x coordinateDX = y coordinate
Returns:Nothing
33h 7
Set horizontal limits for pointer
Call with:AX = 0007hCX = minimum x coordinateDX = maximum x coordinate
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Interrupt Service Service
33h 8
Set vertical limits for pointer
Call with:AX = 0008hCX = minimum y coordinateDX = maximum y coordinate
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1) Program to find whether mouse driver is loaded or not.
#include
Void main(){
union REGS i,o;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
printf("No Mouse Available.....");
else
printf("Mouse Available......");
getch();
}
The above program declares two variables of type union REGS.union REGS, which is
declared in dos.h, contains two structures(struct WORDREGS x, struct BYTEREGS
h).These two structures contain some 1-byte long and 2-byte long variables which
indirectly represent CPU's registers. By placing 0 (sub-function) in ax register and
invoking mouse interrupt(33h),we can check whether mouse driver is loaded or
not.we used int86() function to invoke the interrupt.int86() takes 3 arguements:
interrupt no and two union REGS type variables. If mouse driver is not loaded, it
returns 0 in ax register. All return values are accessed using 'o' i.e why we have
o.x.ax==0 in if statement.
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2) Program to show the mouse pointer.
Our first program only reported mouse driver loaded or not.Even if driver is
avilable,we have no signs of mouse pointer.To view mouse pointer,we have to use
sub-function 1.Look at the program presented below.
#include
Void main()
{
union REGS i,o;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{printf("No Mouse Available.....");
exit();
}
i.x.ax=1;
int86(0x33,&i,&o);
}
The above program is same as our first program except for the last few lines. We have
placed 1 in ax register and invoked mouse interrupt to see the pointer. Since we are in
text mode, our pointer is a rectangular box. We can observe an arrow if we switch tographics mode.
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3) Program to hide the mouse pointer.
Mouse cursor still remains, even after our program is terminated. Look at the
following program.
#include
Void main(){
union REGS i,o;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No Mouse Available.....");
exit();
}
i.x.ax=1;
int86(0x33,&i,&o);
gotoxy(24,23);
printf("Press any key to hide mouse cursor...");
getch();
i.x.ax=2;
int86(0x33,&i,&o);
gotoxy(10,23);printf("Mouse cursor is hidden !! Press any key to
terminate the program ...");
getch();
}
The above program uses sub-function 2 and invokes mouse interrupt to hide the
mouse pointer.This function is quite a useful function,when writing programs that
draw a line or rectangle as we move the mouse. While writing those programs we
don't want mouse pointer to erase what we draw hence we hide the pointer.
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4) Program to show the position of the mouse pointer.
For writing any useful program with mouse support,we need to know the (x,y) co-
ordinates of the mouse position.The below program prints the position of the
mouse,as we mouse the mouse.
#include Void main()
{
union REGS i,o;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No Mouse Available...");
exit();}
i.x.ax=1;
int86(0x33,&i,&o);
gotoxy(25,23);
printf("Press any key to exit...");
while(!kbhit())
{
i.x.ax=3;
int86(0x33,&i,&o);gotoxy(2,2);
printf("x->co-ordinate=%d \n y->co-
ordinate=%d ",o.x.cx,o.x.dx);
}
i.x.ax=2;
int86(0x33,&i,&o);
}
In the above program we have a while loop.This loop continues until a key is hit.In
loop,we used sub-function 3 and invoked mouse interrupt. Sub-function 3 returns X->co-ordinate in cx register and Y->co-ordinate in dx register.printf statements prints x
and y co-ordinates as long as the loop continues.Maximum screen resolution for
mouse in text mode is 640x200 and in graphics mode is 640x480.
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5) Program to print which mouse button is pressed.
Knowing which button is pressed is very important task.The program below prints
which button is pressed as soon as we press any button.
#include
Void main(){
union REGS i,o;
int button;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No mouse available....");
exit();}
i.x.ax=1;
int86(0x33,&i,&o);
gotoxy(24,23);
printf("Press any key to exit....");
while(!kbhit())
{
i.x.ax=3;
int86(0x33,&i,&o);
button=o.x.bx&7;
gotoxy(23,11);
switch(button)
{
case 1:
printf("Left button pressed");
break;
case 2:
printf("Right button pressed);break;
case 4:
printf("Middle button pressed);
break;
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case 3:
printf("Both buttons pressed);
break;
case 5:
printf("Left and Middle buttonspressed);
break;
case 6:
printf("Right and Middle buttons
pressed");
break;
case 7:
printf("All the three buttons
pressed);
break;
default:
printf("No button pressed....");
}
}
i.x.ax=2;
int86(0x33,&i,&o);
}
The above program is same as the previous program except we have little extra in
while loop.In while we used the same sub-function 3 and invoked mouse
interrupt.This subfunction even returns button press information in bx register.Entire
button press information is stored in the first 3 bits of the bx register.So we ANDED
bx with 7 to separate the first 3 bits and stored them in button variable.
If the first bit's value is 1 then the left button is pressed,if the value is 0 then it is not
pressed.If the second bit's value is 1 then the right button is pressed,if value is 0 then
it is not pressed.If the last bit's value is 1 then the middle button is pressed,if value is 0
then it is not pressed.
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6) Program to set the position of the mouse pointer on the screen.
Sometimes we need to set the position of the mouse pointer, just as we set the position
of the keyboard's cursor using gotoxy().The following program sets the pointer to
(x=150,y=100) position on the screen.
#include Void main()
{
union REGS i,o;
clrscr();
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No mouse available");
exit();}
i.x.ax=1;
int86(0x33,&i,&o);
i.x.ax=3;
int86(0x33,&i,&o);
gotoxy(1,1);
printf("Current Position:x=%d y=%d,o.x.cx,o.x.dx);
gotoxy(15,23);
printf("Press any key to set the mouse pointer to(150,100)...");
getch();
i.x.ax=4;
i.x.cx=150;
i.x.dx=100;
int86(0x33,&i,&o);
gotoxy(15,23);
printf("Cursor is set ... press a key to exit);
getch();}
In the above program,we use sub-function 4 to set the pointer's position. We set the
X->co-ordinate by placing a value in the cx register and Y->co-ordinate by placing a
value in the dx register.
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7) Program to switch to graphics mode.
The program below switches text mode to graphcs mode.After executing this
program,observe the mouse pointer.Now,it's in an arrow shape. Try to execute
program-4 in graphics mode and observe the maximum screen resolution for mouse is
increased to 640x480.
#include
#include
Void main()
{
int gd=DETECT,gm;
union REGS i,o;
initgraph(&gd,&gm,"c:\\tc\\bgi");
i.x.ax=0;int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No Mouse Avaialable..");
restorecrtmode();
exit();
}
i.x.ax=1;
int86(0x33,&i,&o);
outtextxy(100,400,"Mouse Pointer in graphics
mode!!Press any key to exit");
getch();
i.x.ax=2;
int86(0x33,&i,&o);
restorecrtmode();
}
In the above program,we used standard library function initgraph() to initializegraphics system.This function takes 3 arguments;graphics driver, graphics mode,path
to the driver.By using DETECT,we tell the function to select a suitable driver by
itselt.When DETECT is used,no need to assign anything to graphics mode.Path is null
since the driver files are located in the current directory.This function initializes
graphics system and when the program terminates we come to text mode by using
restorecrtmode() function.
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HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 44 -
8) Program to restrict the mouse pointer within a boundary.
Sometimes,in our program,we need to restrict the mouse pointer with in a screen
boundary.In order to do that,we need to specify the top,left co-ordinates as well
bottom,right co-ordinates.Sub-functions 7,8 are used to limit the pointer within a
boundary.Look at the following program.
#include
#include
main()
{
union REGS i,o;
int gd=DETECT,gm;
initgraph(&gd,&gm,"c:\\tc\\bgi");
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
restorecrtmode();
printf("No Mouse Available.....");
exit();
}
rectangle(99,49,501,151);
i.x.ax=1;
int86(0x33,&i,&o);
i.x.ax=7;i.x.cx=100;
i.x.dx=500;
int86(0x33,&i,&o);
i.x.ax=8;
i.x.cx=50;
i.x.dx=150;
int86(0x33,&i,&o);
while(!kbhit())
;
i.x.ax=2;int86(0x33,&i,&o);
restorecrtmode();
}
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8/2/2019 Advance CP II
45/50
HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 45 -
In the above program,sub-fuction 7 is used to specify two x->co-ordinates and sub-
function 8 is used to specify two y->co-ordinates and these co-ordinates form a
rectangular boundary within which mouse is restricted.
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8/2/2019 Advance CP II
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HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 46 -
9) Free-hand drawing.
If you ever wonder,how pencil tool in paint works.Then,the following program shows
how it can be written in C.The following program makes use of some of the sub-
function,which we already disussed above,and shows how they can be used to write
useful programs like free-hand drawing.Just,go through the following program.
#include
#include
union REGS i,o;
main()
{
int gd=DETECT,gm,button,x1,y1,x2,y2;
initgraph(&gd,&gm,"");
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No Mouse is available..");
exit();
restorecrtmode();
}
outtextxy(230,400,"Press any key to exit....");
while(!kbhit())
{
show_mouse();
get_mouse_pos(&x1,&y1,&button);
x2=x1;
y2=y1;
while(button==1)
{
hide_mouse();line(x1,y1,x2,y2);
x1=x2;
y1=y2;
get_mouse_pos(&x2,&y2,&button);
}
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HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 47 -
}
restorecrtmode();
}
show_mouse()
{
i.x.ax=1;int86(0x33,&i,&o);
}
hide_mouse()
{
i.x.ax=2;
int86(0x33,&i,&o);
}
get_mouse_pos(int *x,int *y,int *button)
{
i.x.ax=3;int86(0x33,&i,&o);
*x=o.x.cx;
*y=o.x.dx;
*button=o.x.bx&1;
}
There is nothing in this program to explain.Since you have gone through the
program,you must have understood the logic.
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8/2/2019 Advance CP II
48/50
HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 48 -
10) Line drawing using mouse.
Following program shows how to draw a line interactively using mouse. If you know
how to draw a line,there is no big deal in developing a program that draws a
square.So,carefully observe and understand the following program.
#include #include
#include
union REGS i,o;
char far *p;
void main()
{
Int gd=DETECT,gm,button;
Int x1,y1,x2,y2,prevx2,prevy2,x,y;
initgraph(&gd,&gm,"c:\\tc\\bgi");
i.x.ax=0;
int86(0x33,&i,&o);
if(o.x.ax==0)
{
printf("No Mouse is available..");
exit();
restorecrtmode();
}
while(!kbhit()){
show_mouse();
get_mouse_pos(&x1,&y1,&button);
if(button==1)
{
hide_mouse();
x2=x1;
y2=y1;
save(x1,y1,x2,y2);line(x1,y1,x2,y2);
prevx2=x2;
prevy2=y2;
get_mouse_pos(&x2,&y2,&button);
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HARDWARE INTERFACING USING C
Prepared By: Chirag Gohel E-mail: [email protected] - 49 -
while(button==1)
{
if(x2!=prevx2 || y2!=prevy2)
{
setcolor(BLACK);
line(x1,y1,prevx2,prevy2);x=x1
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HARDWARE INTERFACING USING C
area=imagesize(x1,y1,x2,y2);
p=farmalloc(area);
if(p==NULL)
{
restorecrtmode();
printf("No Memory...");exit();
}
getimage(x1,y1,x2,y2,p);
}
restore(int x1,int y1)
{
putimage(x1,y1,p,OR_PUT);
farfree(p);
}
When drawing lines interactively,we must make sure that the currently drawn line
doesn't wipe off already drawn lines when it intersects them.In order to do that,the
above program uses save and restore functions.These two functions captures and
restores screen contents.