More Bringing up a CPM

From: Dwight Elvey <elvey_at_hal.com>
Date: Tue Jun 1 16:11:34 1999

allisonp_at_world.std.com wrote:
--snip--
> If your running
> an 8080 many of the dram card didn't work well with oder 8080 designs.
> Some like the Vector 48k, will not run at all as they require ta z80 for
> correct refresh..

 These are DRAM boards of two types that I've had working with my
Poly88 that is a 8080 system ( some mods on the CPU card to get refresh
to work ). The IMSAI has the original 8080 processor board.
They seem to hold data fine so it looks like the
refresh isn't the issue. Since the data isn't modified at
all by the DMA, I'd think it was a missing WR strobe or
not getting the address there at the right time.

--snip--
> For those old systems DRAM was the lest reliable generally and most
> statics tended to work ok. DMA... you sure that card is a DMA, very few
> were. Most of the older systems were totally incompatable to barely
> compatable with DMA devices and bus termination for those is a must have.

 I tend to agree here but in this case, I have 4 ea 8K, 4 ea 4K
and one 16K static cards. I can replace this with one 64K card
if I get the DMA write and read to work correctly. As I said,
these cards are old and I've already had failures with less than
20 hours of trying to bring it back up.

--snip--
> You have some basic hardware reliability issues to deal with
> yet and likely bus noise is one of them. The IMSAI was far better than
> the Altair but like most of the older s100 crates terminating the bus was
> not a bad thing and sometimes required for reliable operation.

 It has a terminator card in it. Since this also has voltage
regulators on it, it might even be a source of problems as well.
I'll loke at it as well.
Dwight
Received on Tue Jun 01 1999 - 16:11:34 BST