More Bringing up a CPM

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Jun 1 15:53:34 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 <elvey_at_hal.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Tuesday, June 01, 1999 2:34 PM
Subject: Re[2]: More Bringing up a CPM


>Don Maslin <donm_at_cts.com> 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
>
Received on Tue Jun 01 1999 - 15:53:34 BST