[sebhc] H8 recreation/follow on

[Lee Hart]

>> So... would it make sense to build a *new* H8 kit? Update the
>> design to include all the basic fixes, and use modern parts
>> (74HC instead 74LS, Z80 instead of 8080, modern bytewide
>> memories, etc.).

Jack Rubin wrote:
> I think you left out a few other items - a decent motherboard with
> a good ground plane and active termination

The ground plane is easy to add, as are gold-plated connectors (Trionix
motherboard). But I wouldn't add active termination; this is more of a
band-aid to deal with the extremely fast rise/fall times of old TTL
parts. By using modern 74HCxx parts, these fast edges are gone and so
are the noise problems they create.

> and a switching power supply with regulated output

Frankly, I think the stock linear supply was a good idea. Very simple to
build or fix, inexpensive, and reliable.

You don't want hobbyists building a switching power supply. They are
tricky and somewhat dangerous to work on. And if you buy one, about all
you can get nowdays are el-cheapo offshore junk that won't be working in
a few years.

Another advantage to using 74HCxx logic and CMOS CPU and memory chips is
that power consumption is so much lower than the power supply is even
simpler and cooler.

> and no on-board regulators.

Leaving off the on-board regulators would make it incompatible with the
original H8 boards.

Also, I think the on-board regulators were a good idea. The H8 has very
few power and ground pins on its boards, so there are relatively large
voltage drops between the power supply and the actual chips. On-board
regulators provide cleaner, more stable power to the chips, and fewer
noise spikes on the bus.

They also spread the heat around nicely, instead of concentrating it all
in one spot so you need a fan to cool it.

> My reaction is that I'd like to see more of what we're starting to talk
> about here - modern, low power solutions to replace rare or unreliable
> components, but staying with an original chassis.

This is pretty much what I'm thinking of, too. A 'new' H8 kit, that
looks like and works like the original, but uses modern parts that are
cheaper and easier to get, and that offer performance advantages as
well.

Boards would be interchangeable with the original, so if we develop a
new CPU or memory board, it could be used to "soup up" an original H8.
But the new boards would have extra features; say, a 2/4/8 MHz Z80 CPU
board, 4 megabyte RAM board, etc.

> IDE...

Since the Heath H67 was a SCSI type device and the existing software
already understands it, it may be better to duplicate the H8-37 board
which had both H37 soft-sector and H67 hard drive support. "Small" Mac
hard drives (only 100 megs or so) are SCSI and almost free.

> high-speed serial output and networking capability

High-speed serial is straightforward, just by replacing the 8250 with
the 16550. The software doesn't need to change, until you want to get
the higher baud rates and use its internal FIFOs.

There are 'beige boxes' that convert a serial port into a WiFi wireless
network port. DPAC Technologies ABDB-SE-DP101, for example, is about the
size of a mouse, and has a built-in web server.

> (wanna write a TCP/IP stack for HDOS?

You could; it's already been done for other Z80 computers. For $99 you
can buy an eZ80 demo board that *includes* this software.

> We have a chance to exercise both our collective design/validation
> skills and our collective buying power.

Exactly! And have some fun building things again, instead of just being
appliance operators :-)
-- 
"Never doubt that a small group of committed people can change the
world. Indeed, it's the only thing that ever has!" -- Margaret Meade
--
Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net


--
Delivered by the SEBHC Mailing List