Mike DeMetz <miked@technologist.com> wrote:

> Any one have a routine equivilant to the BS2's Shiftout?

Mike:

This question was asked just a few weeks ago; here's a copy of my
reply:

------- Forwarded Message Follows ------

The straightforward assembly-language translation of this PBASIC
fragment:

    Shiftout DataP,Clock,msbfirst,[counter] ' Send the bits.
    pulsout Latch,1                         ' Transfer to outputs.

is:

        MOVLW   8           ;Setup to shift 8 bits.
        MOVWF   COUNT       ;

    LOOP:

        BCF     DataP       ;Assume the next bit is a 0; pull the
                            ;DataP pin low.

        RLF     counter     ;Shift the next bit into the carry.
        SKPNC               ;If it really is a 0, skip ahead.
        BSF     DataP       ;Otherwise, pull the DataP pin high.

        BSF     Clock       ;Pulse the Clock line (the NOP may not be
        NOP                 ;necessary; check your device's timing
        BCF     Clock       ;requirements).

        DECFSZ  COUNT       ;Have we shifted all 8 bits out?
        GOTO    LOOP        ;if not, loop back and sjift another.

        BSF     Latch       ;Otherwise, pulse the Latch line.  Again,
        NOP                 ;the NOP may be unnecessary.
        BCF     Latch       ;

With the NOPs in place, this routine takes 84 clock cycles to shift a
byte out... So if your clock frequency is 4 MHz, it'll take 84
microseconds.  At 8 MHz, of course, it would take half as long.

------- End of Forwarded Message ------

-Andy

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499