COP888GW

Application Note 982 COP888GW Features and Applications

Literature Number: SNOA343

COP888GW Features andApplications

INTRODUCTION

The COP888GW is a member of National Semiconductor’sCOP888 family of microcontrollers fabricated in M2CMOS™

technology. The device was established using CCM (Config-urable Controller Methodology) design techniques whichprovide a fast and reliable way to create new derivatives fora fast growing and demanding controller market. In additionto the COP888 feature core this controller includes a mathunit to allow fast multiply/divide operations. The controllerhas special timers for motor control allowing it to be used inapplications where enhanced processing power and motorcontrol capabilities are required (as in plotters, robot-arms orinformation systems.)

This note describes the COP888GW microcontroller empha-sizing the powerful new features. The reader will be giveneasy to use macros to take full advantage of the new CCMblocks.

COP888GW KEY FEATURES

• Multiply/Divide Unit

• Two 16-bit capture modules with 8-bit prescalers

• Four pulse train generators with 16-bit prescalers

• Full duplex UART

• MICROWIRE/PLUS™ serial port with interrupt

• 16 kbytes of on-board ROM

• 512 bytes of on-board RAM

• Multi-Input Wakeup pins (8) optionally usuable hardwareinterrupts either on falling or rising edge

• Two 16-bit timers, each with two 16-bit autoreload/capture registers supporting:

— Processor independent PWM mode

— External Event counter mode

— Input Capture mode

• Low EMI

• Two power saving modes: HALT and IDLE

• Fourteen multi-source vectored interrupts

• Software selectable I/O options

• Package:

— 68 PLCC with 56 I/O pins

CAPTURE TIMERS

With its two high speed, high resolution capture timers, theCOP888GW is ideally suited high resolution frequency mea-surement. To give a feeling for the capabilities, Table 1shows the capture timers resolution versus the measuredsignal freuency with a processor clock (CKI) of 10 MHz. Thesampling rate is CKI divided by a 8-bit prescaler. In the table,the prescaler is set to 1 to allow maximum performance. Thisresults in a maximum resolution of 100 ns.

TABLE 1. Capture Timer Resolution vs SignalFrequency

Resolution/16 14 12 10 8

Bits

Max.Frequency

152Hz

610Hz

2.4kHz

9.6kHz

39kHz

The capture timer can be used for a closed loop control in aDC motor. One of the standard COP888 timers (T1 or T2)generates a PWM signal to control the motor. One of thecapture timer modules measures the actual RPM of the mo-tor. A simple algorithm is used to adjust the motor’s speed tothe desired value.

Figure 1 shows a block diagram of a closed loop DC motorcontrol with one capture and one PWM timer. The MOSFETX1 acts as a low-side driver for the motor and controls thecurrent flow. The current through the motor is proportional tothe duty cycle of the PWM signal, generated by T1, at thegate of X1. An optical disk, in conjunction with an LED/phototransistor senses the motor’s RPM. The pulses generated bythe photo transistor are directly fed to the capture timer’s in-put. The capture timer inputs are alternate functions ofPort-L. This I/O-port features integrated schmitt trigger in-puts eliminating the need for external signal conditioning ofthe input signals.

SOFTWARE MODULES

The following section provides a guide to general purposemacros and subroutines to set-up the capture timer and thestandard timers T1 to T2. The fuctions are written as of mac-ros so the user can easily include them in the applicationsoftware.

CAPTURE TIMERS

Capture Timers Setup Routine

This routine sets the capture timer module CCM1 or CCM2to allow input capture of a signal on the respective port pin.

MICROWIRE/PLUS™, M2CMOS™, COPS™ microcontrollers, NeuFuz™ are trademarks of National Semiconductor Corporation.

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FIGURE 1. Closed Loop DCMotor Control Block Diagram

National SemiconductorApplication Note 982Martin EmbacherApril 1995

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Additionally the I/O pins Port L6 for CCM1 and Port L7 forCCM2 are configured as inputs. This macro should beplaced in a separate macro file and included in the sourcecode after the processor specific include file. Figure 2 showsthe source code to include the macros in the applicationsprogram.

The macro is called in the source code as:

__CT __SETUP , __MODULE, __PRESCALER, __EDGE,__INTR

__MODULE is the capture module number

1 = capture module 1

2 = capture module 2

__PRESCALER is the prescaler value the range is 0 to 255.

EDGE selects the input capture edge

0 = rising edge

1 = falling edge

__INTR select if capture interrupt is used

0 = disable capture interrrupt

1 = enable capture interrrupt

The macro will check that all values are in the acceptablerange and warn the user if this is not the case.

An example of the generated code is shown below. Themacro is called to setup capture timer 1 with a prescaler of100 (dec) to capture signals on a falling edge without thegeneration of an interrupt.

Special attention is needed if the interrupts are enabled inthe macro by setting the __INTR directive to one. An appro-priate interrupt handler must be placed elsewhere in thecode. The macro will allow the capture timer to generate in-terrupts, however it will not provide the respective interruptservice routine.

Capture Timer Read Macro

__CT __READ __MODULE __VARIABLE

__MODULE is the capture module number

1 = capture module 1

2 = capture module 2

__VARIABLE is a variable to hold the contents of the cap-ture register

Standard Timer Setup for PWM Output

__TIM __SETUP __NUMBER __CYCLE __TON __INIT

__NUMBER is the timer number

1 = timer 1

2 = timer 2

3 = timer 3

__CYCLE is the cycle time of the PWM signal the range is 0to 65535

__TON is on time of the PWM signal

__INIT is the initialization value

0 = start with low

1 = start with high

Standard Timer Glitch Free PWM Output

This macro is used to provide a glitch free switched PWMoutput with the standard COP8 PWM timer. In the macro in-terrupts are disabled to wait until a PWM cycle is completedand then reload the registers are re-written. Thisproduces — in difference to an interrupt driven routine — aglitch free output of the PWM signal.

__TIM __PWM __NUMBER __CYCLE __TON

__NUMBER is the timer number

1 = timer 1

2 = timer 2

3 = timer 3

__CYCLE is the cycle time of the PWM signal the range is 0to 65535

__TON is on the time of the PWM signalNote: The source of the macros is found in Section Capture Module Macros

on page 5.

DC Motor Control Example

An example for the application of the macros is basic DCmotor closed loop control. The motor drive consists of thephases start and run. During start, the motor’s speed in-creases up to the maximum speed set by speed__max. Dur-ing run, the speed is kept around speed __max. The slope ofspeed increase is set by speed__plus and the maximum al-lowable speed increase or decrease during run is set byadj__speed. The speed update cycle time may be controlledby the IDLE timer, generating an interrupt every 4096 tC.

.incld cop888gw.inc

.incld gw_macros.inc

.sect main_prog,rom

..

..

.end

FIGURE 2. Including a Macro Into Source Code

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FIGURE 3. __CT__SETUP Resulting Code

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Figure 4 shows the flowchart of a simple closed loop DC-motor control. The macros can be used to setup the timesand to read the current speed value.

Pulse Train Generators

The COP888GW contains four independent pulse train gen-erators designed for stepper motor control. The pulse traingenerator provides a programmable number of 50duty cycle pulses on the output pin. Depending on the exter-nal sequencer logic these timers can be used for regularstep control or for microstep driving.

If the user does not require pulse train outputs on all pins thepulse train generators can be used as four independent tim-ers with interrupt capability.

Microstepping is used in applications where the step sizeshave to be very small to allow smooth transitions from onestate to another. Special microstep drivers and motors have

been developed. These devices turn the applied pulses intocurrent steps to run the motor. The standard input of thesedrivers is a pulse train as generated by the COP888GW mi-crocontrollers. To show the basic stepper motor control cir-cuit a standard stepper motor drive circuit is discussedbased on a four-phase motor. Figure 5 shows the waveformrequired to control a standard motor. CLK is the pulse traingenerated by the pulse train generator, PH1–PH4 are theoutputs to the motor drivers. These signals can be generatedby using a simple shift/rotate register.

Figure 6 shows an application circuit for a bidirectional step-per motor. The shift register is loaded under software controland then the pulse train is started. More than one motor canbe connected in the same manner. Each motor gets its ownsequencer the setup bus signals are common for every se-quencer. Two control signals, unique for every motor, selectthe direction and the mode of the sequencer. Mode can beload new pattern, shift left and shift right. The circuit shownabove is capable of controlling low current stepper motorsused in some applications, if a higher output drive is requiredappropriate driver stages should be used.

As stepper motors usually have some inertia the pulse trainstarts up slowly and increases its frequency, under softwarecontrol, up to full step speed. The same scheme as shown inFigure 4 can be applied if increase speed is replaced by in-crease pulse train frequency and decrease speed accord-ingly to decrease pulse train frequency.

Pulse Train Generator Routines

The first routine sets up the pulse train generators PT1–PT4.Additionally the respective output pins Port E0 for PT1, PortE1 for PT2, Port E2 for PT3 and Port E3 for PT4 can be con-figured if the user needs to output the data.

Pulse Train Generator Setup

__PT __SETUP __MODULE, __PRESCALER, __PULSES,__OUT, __INTR, __RUN

__MODULE is the pulse train module number

1 = pulse train module 1

2 = pulse train module 2

3 = pulse train module 3

4 = pulse train module 4

__PRESCALER is the prescaler value the range is 0 to65535. __ PULSES selects the number of pulses: 0 to65535.

__OUT enables or disables pulse output

0 = output disabled

1 = output enabled

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FIGURE 4. Basic DC Motor Control Loop Flowchart

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FIGURE 5. Standard Stepper MotorControl Waveform (Two Phases On)

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FIGURE 6. Simple Stepper Motor Sequencer

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__INTR select if an interrupt is generated on completion ofthe pulse generation

0 = disable interrupt

1 = enable interrupt

__RUN selects if the pulses are output directly after initializa-tion or at a later time.

0 = don’t start pulse train generator

1 = start pulse train generator

The macro will check that all values are in the acceptablerange and warn the user if this is not the case.

Pulse train output:

The second routine loads a new number of pulses into thepulse train registers and starts the generation. Setting re-garding interrupts and output are not affected. The macro iscalled in the source code as:

__PT __CHANGE __MODULE,__PULSES

__MODULE is the pulse train module number

1 = pulse train module 1

2 = pulse train module 2

3 = pulse train module 3

4 = pulse train module 4

__PULSES selects the number of pulses: 0 to 65535.

MULTIPLE/DIVIDE

The device contains a multiply/divide block to speed up themultiply/divide operations. To give an idea about the speedincrease, Table 2 shows a comparison of the standardmultiply/divide operations done in software with the sameoperation performed using the MUL/DIV unit.

TABLE 2. Multiply/Divide Operation Speed

MUL/DIVMUL/DIV

BlockType of Operation Operation in

Software

Multiply 8 x 8 129 tC 11 tCMultiply 8 x 16 243 tC 11 tCDivide 8 x 8 208 tC 14 tCDivide 24 x 8 827 tC 14 tC

Note 1: Comparisons include loading the registers for the MUL/DIV blockand accordingly the RAM cells used for software multiply/divide on standardCOP8 microcontrollers. The actual 16 x 8 multiply operation takes one tC anda 24 x 16 divide takes 2 tC. However for accurate comparison the registersetup times have to taken into account.

The following section provides software modules used to setup the multiply/divide unit and to load the respective regis-ters. Although the MUL/DIV block does not allow signedarithmetic it can be used with some additional software toperform signed operations. The signed operations check fora sign in every number to be divided ormultiplied — performs a sign conversion if negative — doesthe operation and adjusts the output accordingly.Note: These software modules use constants to show the basic operation ex-

ample of loading the MUL/DIV registers. These need to be customizedin the application software.

Macro for unsigne d 8 x 16 multiply

__MUL816U __MUL1 __MUL2

__MUL1 is the 8-bit unsigned multiplier

__MUL2 is the 16-bit unsigned multiplicand

Macro for unsigned 16 x 16 divide

__DIV1616U __DIV1 __DIV2

__DIV1 is the 16-bit unsigned dividend

__DIV2 is the 16-bit unsigned divisor

Macro for signe d 6 x 16 multiply

__MUL816S __MUL1 __MUL2

__MUL1 is the 8-bit signed multiplier

__MU21 is the 16-bit signed multiplicand

Macro for signed 16 x 16 divide

__DIV1616S __DIV1 __DIV2

__DIV1 is the 16-bit unsigned dividend

__DIV2 is the 16-bit unsigned divisor

FURTHER APPLICATION HINTS

It was shown that the COP888GW with its new and en-hanced functions can operate as a system contoller in vari-ous applications. Due to the large number of I/O lines addi-tional features can be included in the system with minimalexternal hardware effort. For example it was shown in appli-cation note AN-673 how a simple two way multiplexed LCDcontrol can be done with a COP8 microcontroller. The fea-ture can be easily adopted to the COP888GW allowing sys-tem e.g. a simple plotter device to be controlled. Another ap-plication example is a climate control system, whereCOP888GW can be used to control the heating process.Control algorithms can be generated with National’s Neu-Fuz™ software package. User interfaces can be done as de-scribed above with LCD drive. Diagnostics is possible withthe on-chip UART.

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CAPTURE MODULE MACROS

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STANDARD TIMER PWM SETUP MACRO

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STANDARD TIMER PWM OUTPUT MACRO

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PULSE TRAIN GENERATOR SETUP MACRO

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PULSE TRAIN GENERATOR CHANGE MACRO

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MULTIPLY/DIVIDE MACROS

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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