Iomec disc drive / HP 2871 Controller

From: Jay Jaeger <>
Date: Wed Jan 21 19:33:17 2004

For those who might want to follow my adventure with the IOMEC disk drive
and controller (aka HP 2870 drive)

At last report, the controller was hung in a state for which the schematics
didn't match the board.

Part of that issue turned out to be an ECO wire I removed which wire-anded
(I haven't quite figured out why it is called a wired-or sometimes, because
in the cases I have seen, if either input is 0 it drags the result down to
zero -- it is a wired-or only in a negative logic sense) the outputs of two
flip-flops together. Putting that wire back got it to advance one more
phase in the state machine.

The next problem is that one of two error flags (also wire "anded") is
inhibiting a flag which would permit advance into the actual write
operation. Temporarily cutting the trace on the circuit board which
brought that trace into the gates indeed allowed the controller to proceed
and write the first sector on a track of a format operation (at least it
transferred the words necessary via DMA to do so -- I have no idea if it
actually wrote anything at this point).

The good news is that the error flag stuff matches the schematic -- so far,
so I have high hopes of tracking that down....

WooHoo.... (and God bless logic analyzers....)

Jay R. Jaeger The Computer Collection
Received on Wed Jan 21 2004 - 19:33:17 GMT

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