I have written this code for my mcp42010 digipot. The pot 
requires spi interface. I modified an i2c code to output sda, 
scl and cs. I have run my code in a sim. and it looks to be 
functioning as coded but I an not get the pot to activate. All 
of the timings with the com require a min 40ns timing. I think I 
have well exceeded the time min. requirement. there is no max 
accept for a 10mhz clock speed. I am sure my clock speed is well 
under 10mhz. I think my prolem is with timing or the order I 
send commands. here is my code, thanks for any help.

bob
I am not sure how to post a doc file. here is my code.



;software serial comm to digipot
;at89c4051 @ 11.059mhz


;Variable Declairation

sda   equ p1.1    ;tx pin
scl   equ p1.0    ;clk pn
cs    equ p1.2    ;chip select
potab equ 0dbh    ;enable pot 0 & 1
pota  equ 0d9h    ;enable pot 0
potb  equ 0dah    ;enable pot 1
cold  equ 00dh    ;pot cold setting 

org 0

Initialize:

   mov    r0,#0ffh    ; set regesters with 1-3 with timing and loop settings
   mov    r1,#04ch
   mov    r3,#00fh
   mov    r5,#cold    ;pot 0 reg
   mov    r6,#cold    ;pot1 reg
   mov    r7,#014h    ;increment pot loop
   setb   cs          ;initialize output pins
   setb   sda
   setb   scl
   acall  etc_iat     ;start

Data_ECT: 

;   acall  delay2
   acall  ECT          ;send ect and iat settings to pot with delays
Data_IAT:
;   acall  delay2
   acall  IAT
   acall  ECT
   

Mainline:
    
    inc    r5           ;increment pot settings prior to writing to pot
    inc    r6
    djnz   r7,data_ect  ;inc. counter & write to pot after inc.
    ajmp   loop

ECT:
                        ; write ect to pot
    mov   a,r5
    clr   cs
    acall txsend
    mov   a,#pota
    acall txsend
;    acall delay
    setb  cs
    ret

IAT:                    ;write iat to pot

    mov   a,r6
    clr   cs
    acall txsend
    mov   a,#potb
    acall txsend
;    acall delay
    setb  cs
    ret

ETC_IAT:               ;write ect & iat to pot
                        
    mov   a,r5
    clr   cs
    acall txsend
    mov   a,#potab
    acall txsend
;    acall  delay
    setb  cs
    ajmp  mainline



txsend:                      ;output data to pot via software spi
   mov    r4,#008h
txloop:
   rrc    a
   mov    sda,c
   clr    scl
;   acall  delay
   setb   scl
   djnz   r4,txloop
   ret

delay:                       ;delays using reg. 0-3



   djnz r0,delay
   ret

delay1:
   
   djnz r0,delay1
   inc  r1
   cjne r1,#0,delay1
   cjne r2,#0,decrament
   mov  r2,#014h
decrament:
   djnz r2,delay1
   ret

delay2:

   acall delay1
   djnz  r3,delay2
   ret

loop:


   acall loop

end