Spring 2006 1

EE 316 Computer Engineering Junior Lab

LCD modules, PROMs, Serial Ports

Spring 2006 2

Topics

Liquid Crystal Display ModulesEraseable Progrmmable ROMsSerial Ports

Spring 2006 3

Liquid Crystal Display (LCD) modules

Majority of the pixel-based alphanumeric LCD module uses the Hitachi HD44780 LCD controller chip.

Makers are: Densitron, Epson, Hewlett Packard, Optrex, or Sharp. Most have 16, 20, 24, 32, or 40 characters by 1, 2, or 4 lines. The LCD module we will use has a single line of 20 characters. Each character is made of 5x7 dot matrix

For more info: http://www.doc.ic.ac.uk/~ih/doc/lcd/

Spring 2006 4

LCD Display To use these LCD module, you have follow the

timing requirement very precisely.

Pay attention to these times Important times

http://www.mil.ufl.edu/imdl/handouts/lcd-faq.htm

Spring 2006 5

LCD Initialization Before you use the LCD, you need to initialize the

LCD with a very precise sequence of instructions. Follow the intialization very accurately

Need to generate a sequence of 8-bit instructions with a minimum timing delay between two instructions

each instruction requires multiple steps• raise the enable signal ‘E’, apply data or

instruction, lower ‘E’, hold data or instruction You may store these values in a PROM and apply to

the LCD with correct times between two instructions.

Spring 2006 6

LCD Initialization Contd. In this example at the end of the initialization the LCD is asked

to return cursor to the home postion and clear previous display. The LCD is then readied for display data (DD) input. The ASCII

code for capital “D” is then sent to the LCD module

Initialization begins here

Initialization ends here

LCD is ready for Display data input

ASCII 0x44 = D

Spring 2006 7

ASCII code

Spring 2006 8

PROM Read only memory

32K x 8 bits or 64K x 8 bits, etc.

Erasable with UV exposure (15-20 mins)

For 32K, 10 address Pins

8 data Pins Pin named Vpp used for

progrmming Chip enable Read enable

Spring 2006 9

Power-On Reset

In most sequential circuits (i.e., circuits that have FF, latch, or counters, memories), the initial state may not be known after the power is turned on.

Use a RC circuit for the Reset or Clear the FFs. Choose the RC values for correct timing.

Spring 2006 10

PC's Serial Ports

● PC's Serial port (RS-232c interface) is also known as the communication (COM)port.● The serial port transmits a byte of data by sending 8 bits separately. It adds a start bit, a stop bit and if desired, a parity bit.● COM ports are bi-directional. Serial ports use a special controller chip known as the Universal Asynchronous Receiver/Transmitter (UART), to function correctly.● Used to connect to Modems, some printers and digital cameras.

Ref: http://computer.howstuffworks.com/serial-port.htm

Spring 2006 11

PC's Serial Port, contd.● Serial cables can be longer than parallel cables.● The RS-232c data uses -3 to -12 V to represent a 1 (called Mark) and +3 to +12 to represent a Logical '0' (called Space). ● Serial data must be converted to TTL/CMOS level for digital circuits.

http://www.beyondlogic.org/serial/serial1.htm#40

Spring 2006 12

PC's Serial Port, contd.● One can use the RS-232 drivers and recievers to transform the RS-232 level to TTL/CMOS level.

http://www.beyondlogic.org/serial/serial1.htm#40

Spring 2006 13

UARTsUniversal Asynchronous Receiver/Transmitter

➔ To use the serial data in digital applications, we need to convert the TTL/CMOS serial data into parallel data using UARTs.➔ Popular UARTs: 16550, 16450 & 8250 series➔ We will use a CMOS based UART: HD-6402. Read the data sheet carefully before using.➔ UARTs use a clock with is 16 times the baud rate of the serial port.

Spring 2006 14

UART Timing & Control Issues

Spring 2006 15

Interfacing a digital system with a PC (another digital system)

PC and its UART and level converter

MAXIM 233 UART

Spring 2006 16

References http://www.doc.ic.ac.uk/~ih/doc/lcd/ http://www.mil.ufl.edu/imdl/handouts/lcd-faq.htm http://computer.howstuffworks.com/serial-port.htm http://www.beyondlogic.org/serial/serial1.htm#40