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Thread: Patching CLOAD in MITS 4.0 4K or 8K basic for a different port

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  1. #1
    Join Date
    Dec 2011
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    Default Patching CLOAD in MITS 4.0 4K or 8K basic for a different port

    Ok here is the dilemma, I’m working on hooking up an OP-80A to an ALTAIR. The challenge I have is the IO card on this machine is a 3P+S configured to look like an SIO-2 at ports 20/21. The problem is that the parallel ports are now at 22/23 and I can’t change them to be anything else without losing the SIO-2 compatibility.

    So here is my question so I can use the parallel input on the 3P+S which is at port 23 and 24. Does anyone know the memory locations to bootstrap either 4K or 8K basic CLOAD commands. I know that deRamp has patched an SSM card’s parallel to port 6 to use CLOAD with basic, but I can’t do that so I need to modify/patch basic in memory itself to get mine working without adding another card to the system.

    Anyone have MITS basic 4.0 patching information?

    Thanks,
    Corey

  2. #2

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    4K BASIC does not have CLOAD or CSAVE commands. In 8K BASIC 4.0, cassette input loop is at 1140h. The output loop is at 114Eh.

    Mike

  3. #3
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    Quote Originally Posted by deramp5113 View Post
    4K BASIC does not have CLOAD or CSAVE commands. In 8K BASIC 4.0, cassette input loop is at 1140h. The output loop is at 114Eh.

    Mike
    Ok so if I use 8K basic, is 1140h the address of the whole routine or the address to change the port for CLOAD?

  4. #4

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    Code:
    1140 : DB 06		"  "		in	006H
    1142 : E6 01		"  "		ani	001H
    1144 : C2 40 11		" @ "		jnz	L1140
    1147 : DB 07		"  "		in	007H
    1149 : C9		" "		ret

  5. #5

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    If you have a PROM card installed, you can use 4K BASIC and a load/save PROM. See BLOAD.ASM here:

    https://deramp.com/downloads/altair/...ad%20&%20Save/

    Adding your 3P+S parallel port would be simple.

    Mike

  6. #6
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    I think I decided since this is for an exhibit at the VCF museum that I'll hook up the OP-80A to a UART (should be simple to wire up since it's only input) and plug it into the back of the ADM3A extension. This way visitors can load programs and see the characters "typed" into basic as they pull the tape though the OP-80A using a tape winder.

    I may need to modify Martin Eberhard's MBLe to "read" an extra character for the SIO-2 like he does for the PIO to let the OP-80A load basic without being so testy on the tape starting position. That's an easy mod, Martin provides the source.

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