More Bringing up a CPM - test-drb@ccmp.vtda.org

1 Jun 1999

Do you know what the nature of the problem is?  Does the DMA simply fail to
write to the DRAMM because it doesn't write to RAM at all, or is it a DRAM
timing failure?  Have you examined the nRAS nWE and nCAS signals to the DRAM
with your 'scope?  Where does this DMA live?  Is this an i8257 on the
controller?

If you can take a look at a repetitive read waveform set on the DRAM chips
themselves, you'll easily see whether the timing is correct.  The critical
things are the relationships between nCAS and valid data and nCAS and nWE.
nWE must end before nCAS.  If the DMA will work on the SRAMs and not the
DRAMs, it's probably a bus timing issue.  Perhaps you have to slow down.

Dick

-----Original Message-----
From: Dwight Elvey &lt;elvey(a)hal.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, June 01, 1999 2:34 PM
Subject: Re[2]: More Bringing up a CPM

...
 Don Maslin &lt;donm(a)cts.com&gt; wrote:
  On Fri, 28 May 1999, Dwight Elvey wrote:

 Dwight,

   My next question is, could someone send me an
image of a
 directory that I could use to build my disk? 
 --snip-- 
  Here is an image of a 2.2 directory from an
8"SSSD disk.  Hope it proves
 useful.  (It is not Imsai.) 
Hi Don
 Thanks a lot. As it was, I didn't need to do anything to start
the directory. If it had the original E5's in it, CPM thinks
it is an empty disk. Clever of DR, wasn't it! I'm learning
more about CPM than most people know anyway.
 I was able to get a the system to the "A>" late Monday
night. I then transfered some files by my simple serial
downloader into the memory and used the SAVE command
to write them to files. I did this for the DUMP, ED,
STAT and ASM commands. DUMP and STAT seem to work
OK but I'm having troubles with ED and haven't tried
ASM yet.
 The ED command has some serious troubles. It allows me to
do "I" and "T" commands but won't do a "L" or
"E" commands correctly.
Saving text to a file is one of the most useful parts of
an editor but being able to move around is number 2 or 3.
Since DUMP works, I'll use that to read back what the file
has in it. If not that, I'll make an image file for CCP, BDOS
and CBIOS. I'll then be able to tell where the problem
lies.
 I've had some issues with RAM loosing data but I not sure
where the problem is yet. This may be my problem. The
RAM boards I have are some older 4K, 8K and one 16K
static RAM boards that make up the needed 64K ( actually
62K ) by the CPM.SYS file I have.
 I have some DRAM boards that I've used with my Poly88.
These are 64K boards and I thought I'd use them but the disk's
DMA doesn't seem to write to them. I'm able to read and write
from the front toggles, just not from the DMA to the RAM.

 Does anyone know what the problem is here? Is there some
timing or pin out issue with DRAMs that would cause this
to happen in a standard IMSAI 8080? I'd really like to use
this DRAM because I trust it more than the statics in the
system, at least until I get things fully functional.

 In any case, I think just getting to the A> prompt is
a major mile stone. I had to completely write a boot loader,
CBIOS, disk formatter and serial data transfer to get this far.
My longest to trouble shot problem was the difference
between JNC and JC used with SUB.
Dwight