[Coco] Bitbanging limits

[Darren A.]

>From: Roger Taylor
>
><snip>
>
>In 8 cycles you can LSR <34 which is 65314, pushing bit #0 into the carry 
>bit, followed by a RORA which pushes the carry bit into the data byte.  
>But, to prevent graphics distortion on a CoCo 1/2, you might have to first 
>set up the PIA's DDR so that bits 1-7 are input bits during the receive 
>routines.  This way, an LSR to that register shouldn't corrupt anything.
>
-

Roger,

Am I missing something?  The following code also executes in 8 cycles:

  LDB   <$22  4 \
  LSRB        2  | 8
  RORA        2 /

The one disadvantage is that you clobber B so you can't use it for some 
other purpose.

Darren

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