HCS08 bit bang on 16-bit DAC register

mylim · ‎09-21-2009

Hi guys,

I'm using QE128 bit bang to a Analog Device's DAC AD5308 which it has a 16-bit register instead of 8-bit. So I guess I can't use the i2c peripheral.

I've managed to write an assembler code for this application. However, I'd like to enhance my code efficiency which I think my code isn't that efficient.

DACDTA     ds.B 2
DACBUF     ds.B 1
DTACNT     ds.B 1

txdac       sthx  DACDTA           ;load data to DACDTA
            lda   DACDTA+1         ;load hi-byte
            sta   DACBUF
            lda   #$00
            sta   SR
txdacnxt    lda   #$07             ;setup data count
            sta   DTACNT
            bclr  SYNCDAC,PTBD     ;clr SYNC to start tx
txdac0      bclr  SCLDAC,PTAD      ;pulse clk
            jsr   TDelay
           
            bset  SCLDAC,PTAD
            lda   DACBUF           ;load data to acc
            asla                   ;left shift acc
            bcs   txdac1           ;chk if carry = 1
            bclr  SDADAC,PTAD      ;if /=1,clr SDA
            bra   txdac2
txdac1      bset  SDADAC,PTAD      ;if =1,set SDA
txdac2      jsr   TDelay
            dbnz  DTACNT,txdac0    ;dec data count to chk byte tx
           
txdac3      brset 0,SR,txdac4      ;chk if hi-byte done tx
            bset  0,SR
            lda   DACDTA+0         ;load lo-byte
            sta   DACBUF
            bra   txdacnxt         ;repeat tx
txdac4      bset  SYNCDAC,PTBD     ;clr SYNC to end tx 
            rts

Please advise.

Thanks.

Regards,

MY

Message Edited by mingyee on 2009-09-21 04:50 PM

http://www.analog.com/static/imported-files/data_sheets/AD5308_5318_5328.pdf

Message Edited by t.dowe on 2009-09-21 08:56 AM

bigmac · ‎09-21-2009

Hello Ming Yee,

The AD5308 actually uses an SPI interface, and it should be feasible to use the SPI hardware peripheral for better efficiency. Simply send the data as two bytes in succession, whilst the SYNC line is held low. The SYNC and LDAC lines would be GPIO pins.

; On entry, H:X = data word to be sent

DAC_send: SYNC_LOW ; Macro

LDA SPI1S

PSHH

PULA

STA SPI1D ; Send high byte

BRCLR SPI1S_SPRF,SPI1S,* ; Wait for transfer complete

LDA SPI1D ; Read register to clear flag

STX SPI1D ; Send low byte

BRCLR SPI1S_SPRF,SPI1S,* ; Wait for transfer complete

LDA SPI1D ; Read register to clear flag

SYNC_HIGH ; Macro

LDAC_PULSE ; Macro

RTS

Regards,

Mac

mylim · ‎09-22-2009

Hi bigmac,

I guess i cant use SPI interface as the only spare port i have on the pcb is i2c. Guess I will have to deal with the bit bang method.

I will take the SPI example for the next version of PCB which i am able to cater spi for it.

Thanks.

Regards,

MY

bigmac · ‎09-22-2009

Hello Ming Yee,

For the bit-bang version, my approach would probably be a little different than yours. I would tend to use the stack, rather than create RAM variables. Additionally, the shift process could be tackled as a single 16-bit word, rather than two separate bytes. This should make the code a little less complex.

The following code demonstrates this approach. I have also created macros for the hardware interface, to make the code a little easier to follow. It also means that, should the hardware configuration ever alter, only the macros need to be changed to suit the new configuration.

SYNC_LOW: macro
          bclr SYNCDAC,PTBD
          endm

SYNC_HIGH:macro
          bset SYNCDAC,PTBD
          endm

CLK_LOW: macro
          bclr SCLDAC,PTBD
          endm

CLK_HIGH: macro
          bset SCLDAC,PTBD
          endm

SDO_LOW: macro
          bclr SDADAC,PTBD
          endm

SDO_HIGH: macro
          bset SDADAC,PTBD
          endm

TXDAC:    lda    #16            ; Bit count
          psha                  ; (3,sp)
          pshx                  ; LS byte (2,sp)
          pshh                  ; MS byte (1,sp)
          CLK_LOW               ; Initialise clock state
          SYNC_LOW              ; SYNC low to enable send

TXD1:     CLK_LOW               ;[5] Strobe current data

          ; Left-shift data word
          lsl    2,sp           ;[6] LS byte
          rol    1,sp           ;[6] MS byte

          ; Set serial data output bit state
          bcs    TXD2           ;[3]
          SDO_LOW               ;[5] SDO = 0
          bra    TXD3           ;[3] Branch always
TXD2:     SDO_HIGH              ;[5] SD0 = 1
TXD3:
          CLK_HIGH              ;[5] Return serial clock high
          dbnz   3,sp,TXD1      ;[8] Loop for next bit

          CLK_LOW               ;[5] Strobe last bit
          SYNC_HIGH             ; SYNC high to end send
          ais    #3             ; Adjust stack pointer
          rts

Note that the clock period is 38 cycles, so the communications will be very slow (260 kHz for a 10MHz bus frequency). The period allowed for the data to settle is 18 cycles.

Regards,

Mac

mylim · ‎09-21-2009

Hi guys,

This is my updated routine which i found some bug in the earlier one.

Thanks.

txdac       sthx  DACDTA           ;load data to DACDTA            lda   DACDTA+0         ;load hi-byte            sta   DACBUF            lda   #$00            sta   DACF txdacnxt    lda   #$08             ;setup data count            sta   DTACNT            bclr  SYNCDAC,PTBD     ;clr SYNC to start txtxdac0      jsr   TDelay            bset  SCLDAC,PTAD      ;pulse clk                                    lda   DACBUF           ;load data to acc            asla                   ;left shift acc            sta   DACBUF            bcs   txdac1           ;chk if carry = 1            bclr  SDADAC,PTAD      ;if /=1,clr SDA            bra   txdac2txdac1      bset  SDADAC,PTAD      ;if =1,set SDAtxdac2      jsr   TDelay            bclr  SCLDAC,PTAD                          dbnz  DTACNT,txdac0    ;dec data count to chk byte tx             txdac3      brset 0,DACF,txdac4      ;chk if hi-byte done tx            bset  0,DACF            lda   DACDTA+1         ;load lo-byte            sta   DACBUF            bra   txdacnxt         ;repeat txtxdac4      bset  SYNCDAC,PTBD     ;clr SYNC to end tx              rts

Regards.

MY

Message Edited by mingyee on 2009-09-21 08:52 PM

mylim · ‎09-22-2009

Hi can anyone tell me why the code i posted looks so weird ??

I clicked on the Code tab but seems like there is still some HTML issue.

I tried removing it n redo it, i still get the same result.

Please advise.

Thanks.

MY

mingyee wrote:

Hi guys,

This is my updated routine which i found some bug in the earlier one.

Thanks.

txdac       sthx  DACDTA           ;load data to DACDTA            lda   DACDTA+0         ;load hi-byte            sta   DACBUF            lda   #$00            sta   DACF txdacnxt    lda   #$08             ;setup data count            sta   DTACNT            bclr  SYNCDAC,PTBD     ;clr SYNC to start txtxdac0      jsr   TDelay            bset  SCLDAC,PTAD      ;pulse clk                                    lda   DACBUF           ;load data to acc            asla                   ;left shift acc            sta   DACBUF            bcs   txdac1           ;chk if carry = 1            bclr  SDADAC,PTAD      ;if /=1,clr SDA            bra   txdac2txdac1      bset  SDADAC,PTAD      ;if =1,set SDAtxdac2      jsr   TDelay            bclr  SCLDAC,PTAD                          dbnz  DTACNT,txdac0    ;dec data count to chk byte tx             txdac3      brset 0,DACF,txdac4      ;chk if hi-byte done tx            bset  0,DACF            lda   DACDTA+1         ;load lo-byte            sta   DACBUF            bra   txdacnxt         ;repeat txtxdac4      bset  SYNCDAC,PTBD     ;clr SYNC to end tx              rts

Regards.

MY

Message Edited by mingyee on 2009-09-21 08:52 PM

HCS08 bit bang on 16-bit DAC register

HCS08 bit bang on 16-bit DAC register

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