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Re: Autoboot signature and BASIC IO from Peripheral card

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"epoo...@gmail.com" <epooches@gmail.com> writes:

> Does anybody know (or can point me in the right direction) of a byte
> sequence for a peripheral card that will autoboot from the monitor and
> allow for BASIC I/O entry points? As far as I can tell, this area
> overlaps, and you would end up running undocumented opcodes for the
> BASIC I/O.
> For reference, my understanding is that the Auto boot sequence is looking for:
> cn01: 20
> cn03: 00         
> cn05: 03
> cn07: 3c
>
> And BASIC Init, In, Out are at cn00, cn05, and cn07 respectively. I
> think this means $03 (SLO) and $3C (NOP) would be run, which are
> undocumented opcodes. Also, $20 would need to play some part in the
> init sequence, either as a JSR, or address byte, or something. The
> area is so tight that I can't figure out a solution even when running
> the illegal ops. Thanks for any help.

I think those constants are ID-bytes only for disk-controllers, if I
remember right.

For character I/O cards like the Super Serial Card, they do support the
Cx05 and Cx07 entry points, and they do it like:

C100: 2C 58 FF  BIT $FF58   ; known $60 byte; set the V-flag, denoting PR# or IN# entry
C103: 70 0C     BVS $C111   ; boot entry
C105: 38        SEC
C106: 90            ; fake BCC opcode that never branches, but skips the CLC
C107: 18        CLC
C108: B8        CLV         ; clear V-flag, denoting "already initialized" entry
...

Notice how this code has none of those ID-bytes.  But you cannot boot
DOS or ProDOS from a Super Serial Card.  :)

If you wanted something that could handle character I/O and boot like a
disk drive, well, yes, those illegal opcodes are not going to work.


--
Jerry    awanderin at gmail dot com

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Thread

Autoboot signature and BASIC IO from Peripheral card "epoo...@gmail.com" <epooches@gmail.com> - 2021-06-08 11:49 -0700
  Re: Autoboot signature and BASIC IO from Peripheral card fadden <fadden@fadden.com> - 2021-06-08 21:42 -0700
    Re: Autoboot signature and BASIC IO from Peripheral card "epoo...@gmail.com" <epooches@gmail.com> - 2021-06-08 23:51 -0700
  Re: Autoboot signature and BASIC IO from Peripheral card awanderin <awanderin@gmail.com> - 2021-06-08 22:48 -0600
  Re: Autoboot signature and BASIC IO from Peripheral card kegs@provalid.com (Kent Dickey) - 2021-06-10 09:45 -0500
    Re: Autoboot signature and BASIC IO from Peripheral card "epoo...@gmail.com" <epooches@gmail.com> - 2021-06-10 09:19 -0700
      Re: Autoboot signature and BASIC IO from Peripheral card "epoo...@gmail.com" <epooches@gmail.com> - 2021-06-10 12:55 -0700
      Re: Autoboot signature and BASIC IO from Peripheral card fadden <fadden@fadden.com> - 2021-06-11 14:32 -0700

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