topic Re: Bidirectional SPI routine in 8-bit Microcontrollers

HCS08QG8 - Bidirectional SPI routine

FC — Wed, 14 Mar 2007 08:29:24 GMT

Hello,

CodeWarrior simulator does not work for this simple bidirectional SPI. Note, the device is a SPI compatible DAC (MAX548A) and only bytes are tranferred, no reads

The simulator does not set the second SPSTEF flag. The first SPSTEF is set almost immediately due to an idle SPI. Rather, the simulator sets SPRF when the second transfer starts, but its output mode.

void init_DAC(void)
{
unsigned char temp;

CS = LOW;
temp = SPIS;
SPID = 0xFF;
while(!SPIS_SPTEF);
temp = SPIS;
SPID = 0x00;
while(!SPIS_SPTEF);
while(SCLK);
CS = HIGH;
}

Note, CPOL and CPHA are 0 according to the MAX548A datasheet.

Alban Edit: FSL Part Number in Subject line.

Message Edited by Alban on 2007-03-14 11:33 AM

Re: Bidirectional SPI routine

bigmac — Wed, 14 Mar 2007 09:34:26 GMT

Hello,

Whether you use the returned data or not, I believe you will need to read SPID, with SPIF flag set, to prevent an over-run condition. You will also need to wait until SPIF flag is set (for the second byte) before raising CS.

Perhaps the following modified code -

void init_DAC(void)
{
   unsigned char temp;

   CS = LOW;
   temp = SPIS;   /* SPTEF flag assumed already set */
   SPID = 0xFF;   /* First command byte */

while (!SPIS_SPIF);

   temp = SPID;   /* Clears SPIF flag */
   SPID = 0x00;   /* Second command byte */
   while (!SPIS_SPIF);

temp = SPID /* Clears SPIF flag */
CS = HIGH;
}

Regards,

Mac

Message Edited by bigmac on 2007-03-1401:35 PM

Re: Bidirectional SPI routine

FC — Wed, 14 Mar 2007 09:44:25 GMT

I forgot to mention that its a HCS08QG8.

Upon further investigation, a small delay is requred between SCID writes. The simulator indicates the two bytes sent.

void init_DAC(void)
{
unsigned char temp;

CS = LOW;
temp = SPIS;
SPID = CONTROL_BYTE1;
while(!SPIS_SPTEF);

temp = 5;
while(--temp); // delay

temp = SPIS;
SPID = DAC_INIT_VALUE;
while(!SPIS_SPTEF);
while(SCLK);
CS = HIGH;
}

Remark on the SPRF flag, it will get set in single wire bidirectional mode when the BIDIROE is set (output )?

Re: Bidirectional SPI routine

peg — Wed, 14 Mar 2007 10:27:00 GMT

Hi FC,

If this is the case then it would be due to imperfect simulation.

On the actual device if you know there are no pending SPI transfers you can load SPID twice in a row as in:

SPID = CONTROL_BYTE1;
SPID = DAC_INIT_VALUE;

then just hang around till its done to drop the CS. The first write falls through to the shift register faster than you can load the next byte in.

BTW what is:

while(SCLK);

Re: Bidirectional SPI routine

FC — Wed, 14 Mar 2007 10:46:33 GMT

Hello All,

The back to back writes makes sense because it will wake only 2 clock cyles for the first SPSTEF flag to set.

#define SCLK PTBD_PTBD2

while(SCLK);

Maybe not needed, but its to ensure the SPI clock is low before raising the CS line. It is in one of application notes.

Also, the simulator does show the SPTEF flag low on the second write. The SPI clock is set to 1MHz, this flag should be abled to be viewed by single stepping.

Clarrify this, it appears the SPRF flag will get set even when the SPI is set to output in singe wire mode?

Re: Bidirectional SPI routine

peg — Wed, 14 Mar 2007 11:06:15 GMT

Hi FC,

As the simulator, as is usual, steps instructions and not cycles, you will not see the flag as it is on for less than an instruction.

I believe the SPRF flag functions as normal even though valid data is not being clocked in in this mode. This is also because "data finished being shifted in" is exactly the same as "data finished being shifted out"

Re: Bidirectional SPI routine

baddad — Wed, 14 Mar 2007 22:28:35 GMT

Here is the way I have done it using the 9S08AW32. Should work the same.

Note: This was ported from some old 705 code, so the X register is used to manipulate and maintain a stack(used too much in the code to change this).

Hope it helps.

;
; Read in a Word from the EEPROM
; E - TOS = Address of the Word
; R - TOS & TOS+1 = Word Read
; L - A
;

RD_93XX:
LDA SPI1S   ;dummy read to clear flags
LDA SPI1D   ;dummy read to clear Data reg
LDA #$80  ;Add Read Command
STA ,X   ;Save Command Bits
LDA 1,X   ;Load Address from Para Stack
AND #$3F  ;Mask Address Bits
ORA ,X   ;Add Command Bits
STA 1,X   ;Store on Parameter Stack
; write command
PUL_A         ;Load Character from Stack
STA SPI1D      ;Send Character
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;dummy read to clear Data reg
; READ BYTE
STA SPI1D      ;dummy write
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;read byte
STA ,X          ;store byte
DECX        ;Dec Parameter Stack Ptr
; READ BYTE
STA SPI1D      ;dummy write
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;read byte
STA ,X          ;store byte
DECX        ;Dec Parameter Stack Ptr
RTS             ;return

;
; Write to EEPROM
; E - TOS = Address of EEPROM
; TOS+1 & TOS+2 = Word to be Sent
; R - none
; L - A
;

WR_93XX:
LDA SPI1S   ;dummy read to clear flags
LDA SPI1D   ;dummy read to clear Data reg
LDA #$40  ;Write Command
STA ,X   ;Save Command Bits
LDA 1,X   ;Load Address from Para Stack
AND #$3F  ;Mask Address Bits
ORA ,X   ;Add Command Bits
STA 1,X   ;Store on Parameter Stack
; write command
PUL_A         ;Load Character from Stack
STA SPI1D      ;Send Character
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;dummy read to clear Data reg

JSR SWAP   ; Swap Bytes
;write byte
PUL_A         ; Load Character from Stack
STA SPI1D      ; Send Character
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;dummy read to clear Data reg
;write byte
PUL_A         ; Load Character from Stack
STA SPI1D      ; Send Character
BSR WAIT_SPI    ;wait for spi to finish
LDA SPI1D       ;dummy read to clear Data reg
RTS

; WAIT FOR SPI TRANSFER TO COMPLETE
WAIT_SPI:
BRSET SPI1S_SPTEF,SPI1S,WAIT_SPI0 ; Check for Xmit Reg Empty
JSR PAUSE ; No Wait
BRA WAIT_SPI
WAIT_SPI0:
RTS