New find, Heathkit H89 computer.

Tony Duell ard at p850ug1.demon.co.uk
Mon Sep 25 16:28:14 CDT 2006


> There were soft sectored cards but these were uncommon. The

But they do exist, there's one in my Z90.

It's possible to have 2 disk controllers installed at the same time (with
some restrictions). My Z90 has the hard sectored controller linked to the 
intenral drive, and a soft-sectored controller linked to a pair of 
external drives.

> hard sectored drives used a USRT on the controller card. The soft
> sectored used a regular disk controller. The ones in the H8's used

Mine uses a WD1793 and the normal support circuitry.

> a Z80 but I don't think this was the way it was done on the H89.

No, there are only 2 Z80s in the case. One to run user programs, one as 
part od the 'H19 terminal'

> As for CP/M, the machine needed a special logic array chip to do

Wasn't this standard on the H89, etc?

The chip is one of those fusible link PROMs I think. A couple of output
ports are used to set whether the memory map is set up for HDOS or 
CP/M. I have dumps of the memory mapping PROMs (and for that matter the 
other PROMs in the machine) to hand, but you need the schematics if you 
intend modifying things. These ROM iamges came from my machine which 
certainly can run CP/M.

-tony




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