TRS-80 Model 4 help requested

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Feb 27 18:24:57 2003

> Remember, a Model IV needs a boot disk with the Model
> IV ROM file on it or else it won't boot properly. It
> will only boot CP/M+ for the Model IV without this.

Come again????

The M4 (NOT M4P) contains a full set of Model 3 ROMs. It will boot any
model 3 OS (and will then appear as an M3).

When you boot an M4-specific OS, it pages out the ROMs and runs with a
memory map contianing 64K RAM. The M4 OSes therefore make no calls to the
ROM.

The M4P contains only a small boot ROM. It can boot any M4 OS (which
wouldn't use the rest of the ROMs in a true M4 anyway), but can't boot M3
OSes without a _model 3_ ROM image that's found on TRS-DOS 6 disks for
this purpose.

If the machine in question is a desktop M4, there is no problem with the
ROM image file.

> > Is there an easy couple line program I could type up
> > in basic that using INP() and OUT() to test the
> > drive controller to see if it can read from
> > the disk? I _could_ read the tech manual I have,
> > but I tend to be lazy when it comes to re-inventing
> > things that other people already have done.
>
> I don't think so. It might be possible, but I don't
> know how to do that.

BAISC is no way fast enough to read data from a disk. However, you can
talk to the disk controller, and to the drive select latch to turn on
drive motors, move the head around, etc. This will at least tell you if
the drive is doing anything.

>
> > One last thing, if it matters... it seems my machine
> > was upgraded to 128kB RAM. Is is possible that the
> > machine has bad memory that shows up when booting
> > from a disk but not when starting up basic?
>
> If the problem is in the first bank, maybe...

Especially if it's in the first 16K of the first bank. This is the region
that replaces the BASIC ROM when you boot an M4 disk. Try exchanging the
2 banks of RAM (8 chips in each bank) and see if it makes any difference.

-tony
Received on Thu Feb 27 2003 - 18:24:57 GMT