Heathkit H-11 & H-27
Watzman at neo.rr.com
Wed Apr 18 13:31:11 CDT 2007
From: "Ethan Dicks" <ethan.dicks at gmail.com>
I'm still trying to get that H27 drive working. I should check bitsavers
or schematics for the Qbus floppy card. The card itself works to a point -
if I install it in a minimal system (CPU, serial, RAM, boot/terminator), I
can get the system to read in the boot sector from the floppy, but it hangs
about the time RT-11 is running far enough to turn the interrupts on. I
suppose I should also track down an H-11 configuration guide or module list
or installation docs or whatever it came with to ensure I have a happy set
of cards set to happy values. I've checked each chip on the H-27 interface,
so I'm reasonably certain it's not a simple hardware problem; I'm not so
convinced it isn't a jumper or other configuration problem.
Mine came to me with only the enclosure and backplane being native Heathkit.
The rest was 100% DEC (the floppy was never attached while I worked at that
company). If anyone has any H-11 "getting started" docs, I'd appreciate a
As I said previously:
"The H-27 was just two standard 8" drives in a case with a Z-80 based
intelligent controller (WD1771 disk controller chip) that talked to the H-11
using what we would now call a "host adapter" over a proprietary
bi-directional parallel port. The interface and command set wasn't any of
the standards for this type of configuration (e.g. it wasn't SASI or SCSI),
but it used that type of architecture. For a number of years I used an H-27
on an S-100 system with a Tarbell controller by simply disconnecting the
internal intelligent controller and running a 50-pin cable direct to the two
Memorex drives. They were Shugart SA-801 compatible, so it was an easy
configuration to use, the H-27 then being just two drives, a power supply
and a cabinet."
Your interface card (in the H-11/LSI-11) is apparently good. The next thing
to check is the two 8" Memorex drives. Since these are standard 50-pin
cable Shugart compatible drives, this is fairly easy to test if you have
another system .... just disconnect the daisy chain from the internal
controller (the Z-80/WD1771 board in the H-27 cabinet, below the drives
(below the sheet metal that the drives sit on), connect the drives to
another known-good 8" controller and see if they work. If they do work,
then the issue must be in the internal H-27 controller.
That controller is a Z-80 with a WD1771 FDC and, of course, it has it's own
firmware in ROM and it's own RAM (probably a few 2114's). Any of that could
be bad. Also, that board has two modes, selected with a front panel switch,
Heath and DEC (not what they were called, but the switch should be clear).
RT-11 may or may not work in the Heath mode, I'm not sure (but HT-11 most
definitely will not work in the DEC mode, which was really the point of this
exercise). Beyond that, I don't know of a good way to test that board
without something like a Z-80 ICE unit. That type of embedded system can be
very hard to troubleshoot. There may have been some built-in diagnostics,
but I have no information on that at this point.
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