Patches for Altair BASIC?

[Tom Lake]

?Does anyone have the patches necessary to allow Altair BASIC to run on
a Z-80?

I have 4K BASIC 4.0, 8K BASIC 4.0 and Extended BASIC 4.1. The first two
never even get through the sign-on process to display the number of bytes
free. Extended goes all the way through and I can enter programs but it
refuses to set numeric variables (string variable are set correctly):

10 A=4
20 PRINT A

prints 0

Tom Lake

[Henk Siewert]

LET A=4

Henk Siewert

"Tom Lake" <tl...@twcny.rr.com> schreef in bericht
news:i8cjgs$urg$1...@speranza.aioe.org...

[Tom Lake]

"Henk Siewert" <s...@tiscali.nl> wrote in message
news:4cac46e1$0$30704$5fc...@news.tiscali.nl...
> LET A=4
>
> Henk Siewert

Have you actually tried it? Did it work?

Tom L

[Herbert Johnson]

On Oct 4, 9:07 am, "Tom Lake" <tl...@twcny.rr.com> wrote:
> ?Does anyone have the patches necessary to allow Altair BASIC to run on
> a Z-80?

simh.trailing-edge.com/pdf/altairz80_doc.pdf

This documents use of SIMH. Rich Cini has done work on this emulator,
I believe. PDF page 7 says:

SET CPU Z80 - Simulates the Z80 CPU.

Note that some software (e.g. most original
Altair software such as 4K Basic) requires an 8080 CPU and will not or
not properly run on a Z80. This is mainly due to the use of the parity
flag on the 8080 which has not always the same semantics on the Z80. -
end quote

I recall a number of people who have offered Z80 emulators, or Z80
products for the S-100 bus (originated by MITS as the Altair Bus), who
have mentioned this issue. Last time around, it was mentioned I think
by Vince Briel regarding his "ALTAIR 8800micro" kit, with a work-alike
front panel and simulated 8080 CPU. I believe I recall correctly, he
initially emulated a Z80 but could not get Altair BASIC to work, so he
changed to emulating an 8080.

Why not disassemble the 4K program enough, to see where parity may be
a problem? Look for the 8080 instructions that depend on parity versus
the Z80 instructions that use it differently...a Google search for
"8080 z80 parity differences" finds a number of resources.

Herb Johnson
retrotechnology.com

[Kenneth Scharf]

At one time the required patches were known and there were patched
versions of Altair basic around. Also, Microsoft themselves later
released a versions that run on the Z80.

This reminds me of the paper tape software for the Heath H11 computer,
which was really a DEC LSI-11. DEC had some stand alone basic, focal,
editor/assembler software for the PDP-11, but it would NOT run on the
LSI-11 because it relied on access to the status register which was
located in memory space on the UNIBUS. The LSI-11 did NOT have a status
register in memory space, so there were two new instructions added to
read and write the status register. The access of the status register
took a two word instruction on the PDP-11, but was just a single word
instruction on the LSI-11.

I was working at DEC at the time that Heath sold the H11. I found a
copy of the paper tape software and tried to load it on the LSI-11, it
would run and crash. Using the micro-odt (the LSI-11's built in 'front
panel' octal debugger) I could modify the instruction that caused the
crash (a read or write to the non-existing UNIBUS address of the status
register) and replace it with a read or write status register and a NOP.
Eventually, I found all the bad instructions and had a working LSI-11
basic. Heath probably did the exact same thing. I however, made use of
an RK05 (12" hard disk) DOS to save and reload the basic instead of
using paper tape.

I should also point out that there were several variants of the 8080,
and not all of them would run Altair basic either! The AMD 8080 was
nearly identical to the Intel as was the one made by TI. All of them
had slight quirks as to the status bits following certain instructions.
The NEC 8080 had much the same issues as the Z80 so would not run
Altair basic. I remember writing a CP/M program that would identify
which make of 8080 or Z80 processor you were running. I don't think
that the NEC 8080 would even run CP/M (without patching) though. The
program would also identify between a Zilog Z80, and NSC800 processor
(both Z80 instruction compatible, but the NSC800 had an 8 bit refresh
register instead of a 7 bit as the Z80. The NSC800 was a Z80 with a bus
structure similar to the 8085). I don't remember if I also looked for
the Z180 processor.

[Tom Lake]

At one time the required patches were known and there were patched
versions of Altair basic around. Also, Microsoft themselves later
released a versions that run on the Z80.

Yes! These are exactly what I'm looking for. I was hoping someone here
might remember exactly what those patches were and/or have a copy of the
patched BASICs. You don't happen to remember what version of BASIC
Microsoft released that already runs on a Z-80 do you?

Tom Lake