Heathkit H89a

From: Tom Uban <uban_at_ubanproductions.com>
Date: Mon Aug 26 21:44:00 2002

So now that I know some other name and numbers to look under, I've been
able to find quite a few pages about heathkit h88 h89 and zenith z89 machines.

--tom

At 11:46 PM 8/26/2002 +0100, you wrote:
> >
> > I acquired a Heathkit H89a this last Saturday at a local hamfest, but it
> > did not come with any manuals. Does anyone have one that I can copy
> > and return or which you would be willing to copy for me? Or better yet,
>
>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.
>
>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.
>
>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.
>
>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.
>
>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.
>
>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...
>
>-tony
Received on Mon Aug 26 2002 - 21:44:00 BST