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'SPI code for BS2 (other) interface'
1998\06\19@100942 by

picon face
Hi everyone,

I want to interface a BS2 to a PIC 16f84 via the BS2 shiftin/out command,
using a clock to synchronize bit transfer. I have used the BS2 to talk to a/d
converters and other using SPI interface. Now I want to create a PIC assembly
routine that can be on the receiving end.

Does anyone have some SPI or similar source code that shows how to do this?

I have asked before with no luck, it must be regarded as "precious". I know
the BS2 pulses the clock line for 14us then waits 46us for the next pulse. The
clock pulses are used to synchronize the bit transfer. I haven't found
anything on the web.

Any help or direction appreciated.

1998\06\22@030120 by Dr. Imre Bartfai

Hi Nichole,

here is a routine I use to receive the SHIFTOUT-ed data from the other

' This program receives a binary byte sent by SHIFTOUT (MSB first)
' and displays it as decimal value on three 7-segment LED display.
' The order is 100, 10, 1, i. e. ones send first.
' They are driven by three daisy-chained 74164 ICs. The data
' coming by another shiftout. The input Clock is RB.0, input Data
' is RB.1
' As a special feature, a timeout for spurious clock pulses is
' also implemented.
' The transparent mode flag is always on, and a rescaling will be taken.
'   DEVICE  16C622

DEFINE  OSC     16

RCVD    VAR     BYTE    'the byte received
RDY     VAR     PORTB.2 'the Ready Flag
CLK     VAR     PORTB.0
RDYLED  VAR     PORTA.4 'the Ready LED
DP100   VAR     PORTA.2
DP10    VAR     PORTA.1
DP1     VAR     PORTA.0
TRNP    VAR     PORTB.3 'Transparent Mode flag

TEMP    VAR     BYTE    'temporary for EMIT
CTR     VAR     BYTE    'the bit counter
TEMPW   VAR     WORD    'temporary rescaled value
em_1    var     byte    'byte to be shift out

INCLUDE "modedefs.bas"

OPTION_REG = %11000100  'TMR0 prescaled w/32 = 3.2 msec at 10 MHz

TRISB.2 = 0             'Ready Flag as Output
RDY = 1                 'at start not ready
CMCON = %00000111       'turn all comparators off (622)
TRISA = %11101000       'Ready Led & DP's as Output
PORTA = 0               'D.P. test

EM_1 = 0                'full zero: '8'
GOSUB Emit_3
PORTA =  %00000111      'clear D.P.'s
EM_1 = $3               '0'
GOSUB Emit_3

       bcf     _RDY
       bcf     _RDYLED
       movlw   8               ; prepare receive routine
       movwf   _CTR
ClkWait                         ; main receiving routine
       btfss   _CLK            ; Wait for Clock
       goto    ClkWait

       clrf    TMR0
       bsf     _RDY            ; receiving begun
       bsf     _RDYLED
       goto    Rcvr

ClkLo   btfsc   _CLK            ; Wait for Clock
       goto    Rcvr            ; CLKHI received
       movf    TMR0,W          ; check for TimeOut
       andlw   80h             ; overflow test
       btfss   STATUS.Z        ; skip if zero
       goto    _MainLoop
       goto    ClkLo

Rcvr    bcf     STATUS.C        ; clear carry
       btfsc   _DIN            ; copy DIN into Cy
       bsf     STATUS.C
       rlf     _RCVD           ; into Received
ClkHi   btfsc   _CLK            ; now wait for Clock low
       goto    ClkHi           ; no Wdt needed!
       decfsz  _CTR            ; loop
       goto    ClkLo

--------[cut here]------------

The result is now in _RCVD

I made a h/w handshake to signal the sender I'm ready to receive: it is
the _RDY line.


On Fri, 19 Jun 1998, <Nichole Petty> wrote:

{Quote hidden}

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