Re: Applesoft BASIC PRINTs 7 bit data?

[dalloff@gcfn.org (Dave Althoff Jr)]

Heynony (nospam@noway.com) wrote:
: "Joel" <joelbuckley54.nospam.@hotmail.com> wrote:

: > If you just want to do file transfer to another computer, there are plenty
: > of modem programs to handle that.

: No, I'm running a program that periodically needs to talk to a device 
: that has a hard wired and immutable 8 bit data length. At least 
: apparently immutable, I'm looking into that as well.

Applesoft does all kinds of bit-banging on output, and I am not certain at
what stage that bit-banging is happening.  Recall that for the screen,
low-bit ASCII is flashing text, high-bit ASCII is normal.  I think
Applesoft *sends* 8 bits, but bit 7 bears no resemblance to reality.  8-)

In any case, the solution to your problem should be an easy one.  If you
are able to talk to your device using a PRINT statement, then clearly your
device has hooked itself into CSW ($36-37).  If that is the case, then a
quick bit of assembly code should solve your problem:

*300: 00        DS  1     ;Character to be sent
*301: AD 00 03  LDA $0300 ;Get character from $0300 = 768
*304: 20 ED FD  JSR $FDED ;Send it to COUT
*307: 60        RTS       ;Back to BASIC

Alternatively, it's short enough to POKE into place:

]1 POKE 769,173:POKE 770,0:POKE 771,3:POKE 772,32:POKE 773,237:POKE
     774,253:POKE 775,96

To use it, POKE your 8-bit character into 768 and CALL 769:

60000 CH%=ASC(Q1$)+128:POKE 768,CH%:CALL 769:RETURN

If your device is following the rules, then upon initialization it should
insert itself into the output hook at CSW (which is called by COUT at
$FDED) and then return control to the previously installed device at CSW
(usually DOS or BASIC.SYSTEM).  In fact, I think DOS/BASIC.SYSTEM re-hook
themselves to be first in line, but they pass the unmunged character value
to your character handler.  So no fancy machine code is needed, just a
call to COUT that bypasses Applesoft.

Normally PRINT does its own bit-banging and then calls COUT; by bypassing
PRINT and calling COUT directly you can control the value that comes out.

I hope that makes some kind of sense!  I've been trying to write this
message for the past three hours now, but I can't seem to get five minutes
of uninterrupted keyboard time today...

--Dave Althoff, ][.
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