Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ico!isis!scicom!fox
From: fox@scicom.AlphaCDC.COM (David L. Fox)
Newsgroups: comp.sys.tandy
Subject: Tandy 6000 hard disk replacement
Keywords: Seagate ST251
Message-ID: <2645@scicom.AlphaCDC.COM>
Date: 16 Jan 90 07:17:52 GMT
Organization: Foleda Enterprises, Golden, Co.
Lines: 49


	I am still trying to get a Segate ST251-1 (6 heads, 820 cylinders)
to work with my Tandy 12/6000. Thanks again to all who replied to
my earlier message. I believe I have correctly handled all the points
you raised.  I have covered pin 2, the drive select jumper is correct,
Tandy's write protect weirdness in the data cable is working, and I
have covered pin 7 of the data cable.
 
The drive still will not get past the power on boot sequence.  According
to the Tandy service manual the boot ROM will seek in 5 tracks and then
issue a restore command to find track 0. I have been looking at the 
signals between the drive and controller and here is what I see: 
 
1.  Controller asserts DIRECTION IN.
2.  Controller generates 5 step pulses.
3.  Drive releases TRACK0 and SEEK COMPLETE.
4.  After approx. 15 ms drive asserts SEEK COMPLETE.
5.  Controller releases DIRECTION IN.
6.  Controller generates one step pulse.
7.  Drive releases SEEK COMPLETE.
 
At this point the system hangs, waiting for the drive to complete the
seek.  The drive never asserts SEEK COMPLETE.
 
If I replace the ST251 with a Tandon TM502 (4 heads, 306 cylinders, 
similar to the original 6 headed TM503) every things works normally.
I see events 1 to seven exactly as above but they are followed by:
 
8.  Drive asserts SEEK COMPLETE
9.  6, 7, and 8 repeat 5 times until drive asserts TRACK0.
 
This looks like a bad ST251 except that the drive works fine in an XT clone
and a known good Tandon TM262 also does not work with the Tandy.
 
The only thing I can see wrong with the above is that the 5 step pulses
in #2 are at approx. 2 ms intervals.  This is in the unspecified region
between "buffered seek timing" (<200 us) and "slow step timing" (> 3ms).
Does any one know if this would cause the ST251 to hang in the observed
fashion?  Is there any way to change the step rate used by the boot rom.
(A software only patch would be nice but I could burn a new eprom if I
knew the locations to patch.  I have Z80 Control System Version 3(120)
23-Mar-87.)
 
The above reflects my current thinking about the source of the problem
but I may be completely off the track.  I have explored more than one
blind alley already.  Any and all advice will be welcome.
 
David Fox   fox@scicom.alphacdc.com   { isis | boulder | ncar }!scicom!fox
(303)-278-9859 (voice)