The TRS-80 Journey Continues

Tony Duell ard.p850ug1 at
Tue May 10 22:56:58 CDT 2022

[TRS-80 Model 4P]
> If it will do it with a blank disk, then the statements that it "doesn't
> have ROMs" are more faulty. It obviously has SOME ROMs, to start up enough
> to try to boot.  But, this would tend towards disproving the statements
> that it doesn't have BASIC in ROM.
> And, if it has the "POKE" command, then all sorts of wondrous things
> become more easily available.

I don't have a 4P, only the desktop Model 4 which of course is known
to have 14K of ROM containing BASIC. But I've been reading the 4P
service manual which has a good description of the boot process.

There is 4K of ROM in a 4P, to extend it to a larger ROM would involve
major-ish hardware modifications. So I think we can discount this.
However the boot process checks to see if it's likely that the Model 3
ROM image is needed and if so it will load it from disk very early on
in the boot sequence. So my guess is that the disk that started all
this had a valid and readable ROM image on it, this was loaded, and
there was then an error loading the rest of the OS so the machine ran
said BASIC.

Incidentally, one feature of the 4P boot that I didn't know about is
that it's possible to boot from the RS232 port. That is to download
(plain binary I think) and run a program from there without a disk.


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