Programmer Power Tools/Programmer Power Tools.iso/microcrn/issue_49.arc/6805DEMO.ARC/EXAMPLE.ASM

Assembly Source File | 1989-07-11 | 13KB | 364 lines

*  Micro Cornucopia Magazine Issue #49
*  6805 Controller Example Project Code
*
*  EXAMPLE.ASM
*
*  Sample program showing design of control program, to be run from
*  the EPROM of an MC68HC705 MCU.  The program monitors one channel
*  of A/D, using an MC145041 Serial A/D converter chip.  LEDs are
*  sequenced as needed, depending on the value of the A/D channel.
*
*  The A/D chip connects to the MCU through the Serial Peripheral
*  Interface (SPI).  The chip select line for the A/D is bit 3 of MCU
*  Port C; a low on this line selects the A/D chip.
*
*  Three status LEDs connect to bits 0-2 of MCU port C.  LED1 (port C,
*  bit 0) stays on at all times, to show the program is actually running.
*  LED2 (port C, bit 1) stays on at all times, provided the A/D value
*  stays below $40.  If the value rises to between $40 and $7F, LED2
*  blinks once per second.  If the value rises above $7F, LED2 goes out.
*  LED3 (port C, bit 2) only comes on if the A/D value reaches $80.
*  If the value lies between $80 and $BF, LED3 stays on.  If the value
*  rises above $BF, LED3 blinks once per second.
*
*  The code for routine TIME and much of the code in MAIN comes directly
*  from the example development project in the M68HC05 Microcontroller
*  Applications Guide.  Refer to pages 4-24 for the original listing.
*  The same program is provided by Motorola as Freeware and as source
*  code on the program disc that accompanies the Applications Guide.
*  I would give credit to the original programmer, if I knew who he/she
*  was.
*


*
*  Register equates
*

PORTA    EQU     $00       Port A data register
PORTB    EQU     $01       Port B data register
PORTC    EQU     $02       Port C data register
PORTD    EQU     $03       Port D data register
DDRA     EQU     $04       Data direction, Port A
DDRB     EQU     $05       Data direction, Port B
DDRC     EQU     $06       Data direction, Port C
SPCR     EQU     $0A       SPIE,SPE,-,MSTR;CPOL,CPHA,SPR1,SPR0
SPSR     EQU     $0B       SPIF,WCOL,-,MODF;-,-,-,-
SPDR     EQU     $0C       SPI Data
BAUD     EQU     $0D       -,-,SCP1,SCP0;-,SCR2,SCR1,SCR0
SCCR1    EQU     $0E       R8,T8,-,M;WAKE,-,-,-
SCCR2    EQU     $0F       TIE,TCIE,RIE,ILIE;TE,RE,RWU,SBK
SCSR     EQU     $10       TDRE,TC,RDRF,IDLE;OR,NF,FE,-
SCDR     EQU     $11       SCI Data
RDR      EQU     $11       SCI Receive Data (same as SCDR)
TDR      EQU     $11       SCI Transmit Data (same as SCDR)
TCR      EQU     $12       ICIE,OCIE,TOIE,0;0,0,IEGE,OLVL
TSR      EQU     $13       ICF,OCF,TOF,0; 0,0,0,0
ICAP     EQU     $14       Input Capture Reg (Hi-$14, Lo-$15)
OCMP     EQU     $16       Output Compare Reg (Hi-$16, Lo-$17)
TCNT     EQU     $18       Timer Count Reg (Hi-$18, Lo-$19)
ALTCNT   EQU     $1A       Alternate Count Reg (Hi-$1A, Lo-$1B)

*
*  Following equates are timer values to produce a 50 msec delay
*  using the MCU timing registers.  Use ONLY one pair of values,
*  depending on the MCU timing crystal for the target system.
*

TMRCNTL  EQU     $D4       FOR 2.0 MHZ CLOCK
TMRCNTH  EQU     $30

*  TMRCNTL  EQU     $6A        FOR 1.0 MHZ CLOCK
*  TMRCNTH  EQU     $18



         ORG     $50       START OF VARIABLES IN RAM

TEMPA    RMB     1         TEMP STORAGE FOR ACC
TEMPX    RMB     1         TEMP STORAGE FOR XR

TIC      RMB     1         50 MSEC TICS; 0-19, 20 TICS = 1 SEC
SEC      RMB     1         CURRENT TIME IN SECONDS
MIN      RMB     1         CURRENT TIME IN MINUTES
HR       RMB     1         CURRENT TIME IN HOURS
AMPM     RMB     1         CURRENT TIME (0 = AM, 1 = PM)
DAY      RMB     1         CURRENT DAY (1 = SUN...7 = SAT)


LED1     RMB     1         CONTROL BYTE FOR LED1 (0 = DARK)
LED2     RMB     1         CONTROL BYTE FOR LED2 (0 = DARK)
LED3     RMB     1         CONTROL BYTE FOR LED3 (0 = DARK)


         ORG     $0100     START OF PROGRAM IN ROM

INIT     RSP               INITIALIZE THE STACK POINTER

*
*  Set timer and SPI characteristics.
*

         LDA     #$50      SPI: MCU IS MASTER, 2 USEC CLOCK
         STA     SPCR      WRITE TO SPI CONTROL REG
         CLRA              TIMER: NO INTERRUPTS OR PINS USED
         STA     TCR       WRITE TO TIMER CONTROL REG

*
*  Set up port C, bits 0-2 for output as LED controllers.
*  Clear LED control bytes (turns LEDs off later).
*
*  Set up port C, bit 3 for output as A/D chip select.
*

         LDA     #$0F      BITS 0-3 = OUTPUT, ALL OTHERS = INPUT
         STA     DDRC      SETUP PORT C
         CLR     LED1      SHOW ALL LEDS AS OFF
         CLR     LED2
         CLR     LED3

*
*  Initialize clock to show 12:00 AM Sunday.
*

         CLR     TIC       ZERO THE TIC COUNTER
         CLR     SEC       SET SECONDS TO 0
         LDA     #12       SET HOUR TO NOON
         STA     HR
         CLR     MIN       SET MINUTES TO 0
         CLR     AMPM      SET TO MORNING
         LDA     #1        SET DAY TO SUNDAY
         STA     DAY

*
*              ----- END OF INITIALIZATION -----
*



*
*  MAIN
*
*  This loop gets executed once each 50 msec, based on the
*  MCU's internal timer.  The compare register is loaded
*  with a target value.  When the timer hits that value,
*  bit 6 of the Output Compare Register (OCR) gets set,
*  marking the end of a 50 msec interval.
*
*  At each interval, the timer is reloaded, the time/day clock
*  is updated, and the chain of subroutines at the bottom of
*  the loop is executed.  So long as the chain takes no more
*  than 50 msec to complete, the MCU will stay on-time.
*

MAIN     EQU     *
         BRCLR   6,TSR,MAIN    LOOP HERE UNTIL TIME OUT
         LDA     OCMP+1        LOW BYTE OF OCR
         ADD     #TMRCNTL      CALCULATE NEW TIMER TARGET
         STA     TEMPA
         LDA     OCMP          DO BOTH HALVES OF 16-BIT VALUE
         ADC     #TMRCNTH
         STA     OCMP
         LDA     TEMPA
         STA     OCMP+1        TIMER TARGET RELOADED

         LDA     TIC           GET TIC COUNTER
         INCA                  BUMP IT
         STA     TIC           AND SAVE NEW VALUE
         CMP     #20           DONE ONE SECOND YET?
         BLO     ARNC1         IF NOT, DON'T CLEAR TIC
         CLR     TIC           YES, START A NEW SECOND
ARNC1    EQU     *

*
*  End of the timing loop; following chain of subroutine calls
*  must complete within 50 msecs.
*

         JSR     TIME          UPDATE TIME-OF-DAY CLOCK
         JSR     PROCESS       READ A/D, SET LED CONTROL BYTES
         JSR     LEDS          PROCESS PENDING LED COMMANDS
         BRA     MAIN          DO IT ALL AGAIN

*
*  TIME
*
*  Update the time-of-day clock.
*

TIME     EQU     *
         TST     TIC       Check for TIC=zero
         BNE     XTIME     If not; just exit
         INC     SEC       SEC=SEC+1
         LDA     #60
         CMP     SEC       Did SEC -> 60 ?
         BNE     XTIME     If not; just exit
         CLR     SEC       Seconds rollover
         INC     MIN       MIN=MIN+1
         CMP     MIN       A still 60; MIN=60 ?
         BNE     XTIME     If not; just exit
         CLR     MIN       Minutes rollover
         INC     HR        HR=HR+1
         LDA     HR        For comparisons
         CMP     #13       HR=13 ?
         BNE     ARNS1     If not; skip
         LDA     #1
         STA     HR        Set HR=1
         BRA     XTIME     Exit
ARNS1    CMP     #12       HR=12 ?
         BNE     XTIME     If not; just exit
         LDA     AMPM
         EOR     #%00000001  Invert AM/PM bit
         STA     AMPM      0=AM, 1=PM
         BNE     XTIME     If not AM now; just exit
         INC     DAY       DAY=DAY+1
         LDA     DAY
         CMP     #8        Day rollover ?
         BNE     XTIME     If not; just exit
         LDA     #1
         STA     DAY       Set Day to 1 (SUN)
XTIME    RTS



*
*  LEDS -- Process any pending LED commands, based on the LED
*  control bytes.
*
*  Each LED control byte determines whether an LED is turned on
*  or off.  If the byte is 0, that LED is always turned off by this
*  routine.  If the byte is not 0, the corresponding LED is always
*  turned on and the control byte is decremented.
*
*  If this routine is called each slice (20 times per second), the
*  longest period of time an LED can remain lit without intervention
*  is 255 * 50 msec = 12750 msec or 12.75 seconds.
*

LEDS     TST     LED1      NEED TO TURN ON LED1?
         BEQ     LED1N     BRANCH IF TIME TO TURN OFF
         BCLR    0,PORTC   TURN ON LED1 (ACTIVE LOW)
         DEC     LED1      COUNT THIS 50 MSEC
         BRA     LED2T     GO TEST LED2
LED1N    BSET    0,PORTC   TURN OFF LED1

LED2T    TST     LED2      DO IT AGAIN FOR LED2
         BEQ     LED2N
         BCLR    1,PORTC   USE BIT 1 FOR LED2
         DEC     LED2
         BRA     LED3T
LED2N    BSET    1,PORTC

LED3T    TST     LED3      SAME AGAIN FOR LED3
         BEQ     LED3N
         BCLR    2,PORTC   USE BIT 2 FOR LED3
         DEC     LED3
         BRA     LEDSX
LED3N    BSET    2,PORTC
LEDSX    RTS


*
*  PROCESS -- Change LED control bytes as needed to reflect current
*  status of A/D input.
*
*  If TIC holds a 0 (first 50 msec slice of each second), read channel
*  0 of the A/D and trash the returned value.
*
*  If TIC holds a 1 (second 50 msec slice of each second), read
*  channel 0 of the A/D and process the LED states, depending on the
*  following:
*
*  Value range                    Action taken
*  -----------    --------------------------------------------
*
*   $00 - $3F     Turn LED2 on for one second, turn LED3 off.
*   $40 - $7F     Turn LED2 on for .5 seconds, turn LED3 off.
*   $80 - $BF     Turn LED2 off, turn LED3 on for one second.
*   $C0 - $FF     Turn LED2 off, turn LED3 on for .5 seconds.
*
*  All other values of TIC are ignored by this routine.  Note
*  that LED1 is always on.
*

PROCESS
         LDA     #$FF      GET LONGEST ON-TIME
         STA     LED1      ALWAYS LEAVE LED1 ON
         LDA     TIC       GET CURRENT TIC VALUE
         BNE     PROCS1    BRANCH IF NOT FIRST TIC
         BSR     A2D       LOAD UP CHANNEL 0 VALUE
         BRA     PROCSX    AND LEAVE

PROCS1   CMP     #1        IS THIS THE SECOND TIC?
         BNE     PROCSX    BRANCH IF NOT
         CLRA              LOAD UP CHANNEL 0 AGAIN
         BSR     A2D       AND READ THAT CHANNEL

         CMP     #$40      IS VALUE IN GOOD RANGE?
         BHS     PROCS2    BRANCH IF NOT
         CLR     LED3      TURN OFF LED3
         LDA     #20       TURN ON LED2 FOR 1 SECOND
         STA     LED2
         BRA     PROCSX    AND LEAVE

PROCS2   CMP     #$80      IS VALUE IN FAIR RANGE?
         BHS     PROCS3    BRANCH IF NOT
         CLR     LED3      TURN OFF LED3
         LDA     #10       TURN ON LED2 FOR .5 SECONDS
         STA     LED2
         BRA     PROCSX    AND LEAVE

PROCS3   CMP     #$C0      IS VALUE IN POOR RANGE?
         BHS     PROCS4    BRANCH IF NOT
         CLR     LED2      TURN OFF LED2
         LDA     #20       TURN ON LED3 FOR 1 SECOND
         STA     LED3
         BRA     PROCSX    AND LEAVE

PROCS4   CLR     LED2      MUST BE BAD, SHUT OFF LED2
         LDA     #10       TURN ON LED3 FOR .5 SECONDS
         STA     LED3

PROCSX   RTS


*
*  A2D -- Read selected channel of serial A/D (MC145041).
*
*  Enter with A/D channel number in ACC.  Returns analog value
*  in ACC.  Assumes chip select line to A/D chip is driven by
*  port C, bit 3 (active low).
*
*  Note that the value returned by A2D corresponds to the most
*  recent previous channel number transmitted, not the current
*  channel number!  Therefore, unless you know for a fact that
*  the last channel number you sent was the one you want to read
*  now, you had better call this routine twice, using the same
*  channel number.
*

A2D
         TST     SPSR      CLEAR SPIF
         BCLR    3,PORTC   PULL CHIP SELECT LINE LOW
         ASLA              MOVE CHANNEL NUMBER TO HIGH NYBBLE
         ASLA
         ASLA
         ASLA
         STA     SPDR      SEND CHANNEL TO SPI

SPIFLP   BRCLR   7,SPSR,SPIFLP    WAIT UNTIL COMPLETE
         BSET    3,PORTC   RELEASE CHIP SELECT
         LDA     SPDR      GET VALUE RETURNED
         RTS



*
*  Set up the RESET vector.  This is required for code that will
*  be moved into the MCU's EPROM for later execution.
*

         ORG     $1FFE     RESET VECTOR

         FDB     INIT      POINT TO START OF PROGRAM