22 Sep
2007
22 Sep
'07
8:29 a.m.
Subject: Re: Unknown S100 system
From: "Roy J. Tellason" <rtellason at verizon.net>
Date: Fri, 21 Sep 2007 16:35:41 -0400
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
On Friday 21 September 2007 16:01, Chuck Guzis wrote:
There was a really nice 8085 system on a board that ran CP/M from Autocontrol
the AC-85. Its featurees were a 5mhz 8085, DMA, 64k ram, FDC, 3 serial channels
and a real time clock interrupt. What made it unique is the DMA was there
to support the FDC for full DSDD 8" and it also unburdened the cpu for
background tasks and interrupt servicing.
On 21 Sep 2007 at 14:07, Roy J. Tellason wrote:
Compupro was the one that was hanging out there at the edge of recall... I wonder why they went with that part? I seem to
remember some others
that used it as well, though specifics are not coming to mind at the
moment. I have a bunch of those on hand, and think about doing
something with them from time to time. It's a fairly easy chip to use,
with an eprom and a ram chip and a single address latch, I just haven't
decided yet what I'm gonna do with it.
Compupro 85/88 board; my own Durango F-85 and a host of others. If
you can find some of the support chips (8155, 8755), the parts count
can be very low, given the vintage of the 8085. I may have some of those support chips, too. 8155
(and 8156, which is the
same part with a different select pin polarity if I'm remembering right)
sound real familiar. I have the 8085 Cookbook and a few others that Sams put
out, one covering this text editor and assembler (which I didn't really care
for, but...). No interest in the ROM-based 8355 and I've never seen the
EPROM-based 8755. The relative i/o and RAM address mapping of those parts
gets a little confusing, though, and the book is a bit less clear than it
could be on that aspect of it.
I have tubes of the 8085 support chips (8155, 8156, 8755) they can also be
used with 8048, 8051, 8088 or pairs for the 8086. The Eprom 8755 is easy
to find and still available from various sources.
A system using an 8085, 8155, 8755 has the following:
2k Eprom
256bytes ram
1 Timer (8155)
38 io lines (8755 and 8155)
3 maskable interrupts
1 trap (non maskable interrupt)
SID and SOD lines (serial IO)
It is/was popular in embedded systems and robotics.
They were also available in CMOS and Rad-hard CMOS making them useful
for extraterrestrial systems.
> I suspect that the reason 8088/8085 pairs were
fairly common in
> comparison to Z80/8088 pairs was that timings and buses on the 8088
> and 8085 are *very* similar and getting them to work with 8000-series
> peripherals was very easy. IIRC, one could even replace an 8085 with
> an 8088 (assuming you were restricting it to 64K addressing) with a
> minimum of "glue". Both multiplex the data lines on A0-A7 the same
> way.
Exactly. Also the 8085 was available to at least 6mhz. The 64k/1m
addressing differnce was taken care of with a simple address mapping
scheme for the 8085. Compupro used it as most using the 8088 and later
boards wer more interested in the 16bit cpu rather than any of the
8 bitters so z80/8085 was not an issue as it was a migration tool
and allowed the use of older CP/M software. Most CP/M commercial
software ran the 8080 programming model.
I suspect it
might be easier to substitute an NSC800 for an 8085 if
Z80 functionality is needed than trying to shoehorn in a Z80.
That's another part I have no familiarity with at all at this point in time,
though of course I've heard of it.
With regard to what little programming I've done, the thing I like most about
the z80 is relative jumps, which makes relocatable code easy to do. The
other big deal is the alternate register set and the index registers, which
I really haven't used all that much.
The items that make z80 desireable for programming to me are the repeat
instructions (LDIR) and the loop (DJNZ) plus some of the smaller instructions
that make the CPU more symetrical. It always bugged me that 8080 can load the
SP but storing it required clearing the HL and adding SP to HL.
What makes the 8085 appealing is in small systems it has hardware advantages
like internal clock oscillator, multiple maskable interrupts, two pins for
single bit IO (SID/SOD), easier timing compared to z80. It doesnt hurt that
it's an upward 8080. it also doesnt hurt that faster parts (6mhz) had far
less difficult memory timing than 6mhz z80. It's also common as house
flies still.
NSC800, had a short product life, I don't think National ever got it
faster than 4mhz, production volumes were small and I rarely ever see
one.
8088/86, hardware around it was easy, hated programming it. Always felt
it was an 8080 with a bag on the side and borrowed the worst z80 features.
It's big cache was it's was 16bit and had the ability to address 1mb.
Allison