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TRS-80 model II boot disk

Unfortunately the appointment with Fred Jan to copy disks has changed date.
But still I was very curious about the TRS80 system. I have some 8 inch diskdrives
and floppies in unknown state which came with the TRS80.

- The 801 drive is missing the PCB and it's filtpad (which is used in de TRS now)
...Besides it's an 115V model and can not be used here. Nice for parts.

- The CDC drive which seems to have a different interface.

- The last drive is an 851 which is used in my Xerox 820 II to!

I'd clean the 851 drive, Jumpered it like the ones in the 820. And yes it works in the 820!

According the website from Dave http://www.classiccmp.org/dunfield/img/index.htm
I'd made my own 8 inch setup on an old P75 machine. The 430FX chipset tested to be very useful.

I'd replace the single use dips for a dipswitch version. The settings on
the P75 machine differ from those on the Xerox 820 machine.
01 Shugart jumper.JPG

This is my 34 to 50 pin convertor. (TG43 not used at the moment)
02 FDD interface.jpg

And the total setup for testing...
03 8 inch setup.JPG

Very Very Very curious..... :D:D:D:D:D

Testing in the next post
 
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So the total setup is ready to make bootdisk right? (See posting above)
Well it's not a just copy and you are ready. But Dave made very
nice documentation and help files.

First it did not headload and it didn't move the head also.
After switching some dipswitches the drive seems to do something.
The heads were moving but still not touching the disk. Finaly I got
the good settings and I could format and write a disk.

Well lets test the disk! Hey it sounds like the TRS is doing something too!
64K memory showed up in the display. I did not see that before!
Bzzz KLIK bzz bz KLIK sound like a booting the TRS DOS system.

----------------
BOOT ERROR DM

23
----------------

Now what? euhhh It seems the machine want to show all possible boot messages to me. :-(
Well maybe I'd make an mistake building the TRS DOS disk. This was version 1.2
Well let's try making the TRS DOS 2.0 disk. No... same problem...

The Boot Error DM means a problem in the DMA. Still wondering, is it a
disk problem or is the machine not working properly?

04 boot error DM.JPG

But hey there is also an CP/M disk for it. Lets try this one...
And you'll never believe it. It really boots up CP/M!

05 booting CPM 22.JPG

It boots up in a menu environment. You can exit to the CP/M prompt here.
There are some programs on the disk like memtest.

06 dir CPM 22.JPG

The memory test does not report any memory problems.

07 mem test cmp.JPG

I'm very curious why the TRS-DOS is not booting.
Maybe I do something wrong, but it could also be a machine problem...


Someone have any idea?

Thanks in advance!
Regards, Roland
 
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I'd try to examine which chip is the DMA controller.
I'd expect a number like Z8410 or something familiar.

But no, there are strange numbers onto these chips.
These numbers are exactly the ones in the TRS documentation.
Did Zilog relabel these chips for Radio shack so no one could
use standard components? I think It's a bit strange...

DMA.jpg
IC's.JPG

I presume I can put a standard Z8410 in this place for the DMA controller?

Regards, Roland
 
I assume that you're using TRSDOS specially for the Model II/16. Other versions will not work. I can probably locate the version that I used on my Model 16 if you'd like.
 
Hello chuck

That's a good idea. But the disk images should be
the good ones. I'd got them from daves website too.

I'm wondering if the cp/m mem test also test the DMA.
Changing the DMA chip does not make a change... (Z8410 used)

Regard, Roland
 
In an earlier post you say: "(TG43 not used at the moment)". If some of the data should come from a higher track than 43, it could result in read errors. CP/M only uses the low tracks to boot.

The support for DMA on the FDC is realized by the PIO on that board. That also could be a cause. But then the CP/M boot would also fail, I assume.
 
Hmm, I don't see where in the boot ROM the "BOOT ERROR DM" is issued, so I suppose it must be from within TRSDOS itself. (The boot ROM uses programmed I/O, not DMA).
 
Hello Fred Jan and Chuck,

The booting of TRSdos is only the lower track indeed.
The head does not come to a higher track then 4 or 5 I guess.

I did a little test by changing the DMA controller
for a Z8410 but this does not make a change.
I thought lets remove it and see what will happen.

For TRS DOS:

----------------
BOOT ERROR DM
23
----------------
changes in

----------------
BOOT ERROR DM
13
----------------

And for CP/M it displays:
----------------
LOAD ERROR 3
----------------

So it seems Chuck is right, the messages seem to come from the OS.

It also seems both are using the DMA. But probably not the same segment?

Could it be possible that TRS-DOS is trying to display the TC logo using
DMA into the video RAM? CP/M is only using ascii characters while booting.

I guess I have to find the schematics of the boards...

Regards, Roland
 
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I dont remember my TRSDOS memory map that well, but I DO recall that it tends to load in the 'low-middle' of RAM... while CP/M uses the UPPER area for the system, leaving 0100h-(start of BDOS) available for programs (with the CCP being 'expendable')...
I would suggest that you have memory issues in the lower-middle areas...
I know that you have run memory tests in CP/M, but they might not have covered the whole 64k block...
Or it needs to run longer, perhaps, to find it...

Not much help, I know... :D
 
Hello Leeb,

That is a good point. Maybe the memorytest does not cover the whole memory.
I'm afraid CP/M does not have a universal mem test program because all
CP/M versions are different for any machine?

Regards, Roland
 
According the documentation there should be
an diagnostics diskette for the model II.
Does anyone have an image from this diskette?

Thanks in advance!
Roland
 
Today I've visited Fred Jan in Rotterdam.

My bag was loaded with a box of 8" empty disks.
And also the 8 inch TRS-DOS disks I'd made myself.
(All disk made by the 8 inch setup using the Pentium 75 machine)

The first thing was trying to boot his machine using my disks.
And guess what, it booted TRS-DOS nicely. And also the TRS80 II
testdisk I'd got from from Kevin booted just perfect. Even the test
disk did not boot in my machine either, also BOOT ERROR DM 23

So it is my computer hardware which is having a problem!

Fred Jan has some spare boards from a donor machine which I could borrow.
Tonight I tried to swap these board one by one. And guess what the problem
is in de CPU board. After swapping this board the machine works fine.

So a bad CPU board... Well let's check the easiest components.
The IC's in sockets. Bingo! The Z80 SIO whas the bad one!
TRS has some really weird numbering on the chips but a 8440 works fine.

08 Bad SIO.jpg

09 TRS-DOS startup.JPG

10 DIR.JPG

So this little monster came alive again today!

Regards, Roland
 
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Thanks for the nice reply's and also thanks for the
advice and thinking with me to fix the machine.
I did not know I'd have this soft spot for the model II also ;-)

Regards, Roland
 
Roland Huisman said:
Thanks for the nice reply's and also thanks for the
advice and thinking with me to fix the machine.
I did not know I'd have this soft spot for the model II also ;-)

Regards, Roland
Click to expand...
Old post but I know Roland is still and active member.

I am in the throws of some fun 8" work and Model II repairs. Just curious Roland if you ever repaired that "Boot Error DM"
 
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