Heathkit H89a

From: Tom Uban <uban_at_ubanproductions.com>
Date: Mon Aug 26 18:47:00 2002

At 11:46 PM 8/26/2002 +0100, you wrote:
>Be waned that the hardware manual is a fairly thick book, and has a
>separate pile of sheets that contain the schematics, PCB layouts, and so
>on. It's an excellent manual (as you'd expect from Heathkit), but it
>won't be trivial to copy.

If I can find someone with a spare manual, that would be preferable, but I
am determined enough to do the copying if need be.

>The H88 and Z90 are essentially the same computer. Basically, 'H' models
>are Heathkit, and came as partial kits (the disk drive, CPU board, and
>'terminal logic board' were ready-built, you got to solder up the monitor
>and PSU). The 88 was a cassette-based machine, the 89 has an internal
>disk drive. The 90 has the full 64K RAM as standard. Or at least that's
>how I interpretted the manuals.
>
> > is there an extra copy which would be available for a small cost?
> >
> > Also can someone expound on this computer?
>
>Yes, it's a H19/Z19 terminal with a computer inside. The Z19 is a
>VT52/VT100 compatible terminal using a Z80 as the control processor and a
>6845 for video. That's what's on the 'terminal logic board', which stands
>vertically right at the back of the case.

The front of the machine is badged Heathkit Computer, the back has a label
with Heathkit model H89a series no. 01-43911.

>In the H89 (etc), that's unchanged. There's a CPU board mounted in front
>of the terminal logic board. It contains another Z80 and 48K DRAM. And a
>boot/monitor program in ROM. The computer communicates with the terminal
>via an RS232 link (I kid you not) between the 2 boards.

I believe you.

>Plugged into the CPU board you are likely to find a triple serial board
>(8250-based IIRC) and a disk controller or 2. And maybe a 16K RAM board
>if you've really got a Z90.

I have the 16K RAM board on one side and a stack of three boards. One
seems to connect to the extern disk FR-1 connector and has a FD1797B
controller. The internal disk controller uses an AMI8116 chip. The third
board has three serial ports (as you indicated).

On the back of the machine, there are three RS232 ports, a connector
labeled FR-1 (external floppy) and three locations for options which are
not present (FR-2, 488, and cassette I/O).

>There were several disk controllers. One was certainly for hard sector
>5.25" disks, and used a USRT + a bit of simple logic. Another handled
>double-density soft sectored 5.25" disks -- I think this was based on the
>Western Digital 1793 chip. There was, I think, a 8" drive controller and
>even a hard disk interface.

I guess it looks like the internal drive may be hard sectored. Is the FD1797B
a floppy or hard drive controller?

>Oh yesm, it runs CP/M or HDOS (which is a bit like a DEC OS at the user
>level). I hope you got a boot disk...

Nope, but Don Maslin has CPM. I will have to find HDOS too.

--tom
Received on Mon Aug 26 2002 - 18:47:00 BST