18 Feb
2003
18 Feb
'03
6:36 p.m.
-----Original Message-----
From: cctech-admin(a)classiccmp.org [mailto:cctech-admin@classiccmp.org]On
Behalf Of Tony Duell
Sent: 18 February 2003 00:12
To: cctalk(a)classiccmp.org
Subject: Re: TRS80 Model 1 Level II
You say it's an L2 machine. Does it have the ROM in 2 off 24 pin chips on
the mainboard (one is 8K, the other 4K, and there are some cut-n-jumper
mods), or is it old enough to have the extra PCB with 3 24 pin chips
(eack 4K) and the address decoder?
It's the former - 2 ROMs and 2 DIP shunts.
ROMs. I found
a link to the Tech Ref for the Model 1 -
excellent book, given
Or ROM failure itself? the writing
style it could've been written by me, same sense of
humour - and
Indeed. The introduction is rather amusing... (As you may have guessed, I
have this manual...) Be warned that much of the tech manual is written
assuming you have a L1
machine. I don't know what L2 does if it can't find any RAM, for
example...
It does predictable things along the lines of no ROM; I can't remember the
resulting screen though. The couple of replies I got on comp.sys.tandy also
suggest ROM failure and/or address lines and/or data lines.
With the ROMs pulled, all the address lines should be
toggling (as the
CPU tries to continually push 39 00 onto the stack). You can check this.
Yep, I'm being dense again and struggling to find a good link to ground I
can fasten my probe too; +5V can be got from the right side of C9. Just need
to study the schematics a bit more.
This I now
know.....good job the tests indicate the RAM is
happy! I guessed
when the RAM turned out to be 16 pin chips
instead of the 2114's 18.....
Yes, the M1 uses DRAMs for the main memory. Either 4K or 16K parts.