From: asgard@sparky (J.R. Stoner)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Servo-writing a tape in a tape backup drive---HELP
Keywords: n
Date: 14 Apr 92 18:03:38 GMT
Organization: Heironamous Botch's Murk Works

Here is what I remember after spending about three man-years writing
a backup system for Irwin 110 and 125 tape drives:

The 125 drive (what you have) will not be able to _write_ or format a DC1000
tape, but can _read_ data from a DC1000A tape that was servo-written and
formatted in a 110 drive.  Do not buy DC1000A tape.  Buy DC2000 tape that has
a coercivity value of 650 Oersteds.  3M tape is the only tape that I have
ever certified for use in these drives.

The primary difference between the 110 and 125 drives are in the head
assembly and some minor changes in the control electronics.  The main
difference is the change from an 8-track serpentine arrangement, to a
12-track serpentine arrangement.  The 110 drive typically has a 158-block
track with embedded servo wedge coincident with data and gap area.  The gap
areas are necessary since the drive must be connected through your floppy-
disk controller.  Things like EOT/BOT detection and tape motion commands are
transmitted to the drive via the STEP line on the floppy interface.  The problem
with this system stems primarily from the use of NEC 765/INTEL 8272 controller
chips in the standard XT/AT.  This chip was originally designed for diskettes
of 77 cylinders.  Typical AT floppies now have 80 cylinders and a bug with
the seek/step logic in the chip gets tickled, but I digress.  The Irwin drive
gets the command by means of issuing a "normal" seek command to the 765 such
that the difference of the relative "old" seek position and the new causes the
correct number of STEP pulses to the drive.

The normal layout of data on a tape track implies that the floppy disk model
must be sufficiently simulated to make the 765 happy, su phony index pulses
must be placed at the same time as the servo wedges.  This is _really_ import-
ant.

The drive is commanded to do a servo-write by command 31 (31 pulses, not a
seek to track 31)  Which makes the drive go do its thing for about 14 minutes
(22 for the 125 drive), which effectively ties up the floppy disk bus until
complete.  The drive then attempts to verify the wedges so that they are placed
properly.  A failed attempt stops tape motion and the LED ought to blink at you.

The tricky thing is these Irwin drives sometimes fail to detect a failed
attempt.  The command completes with the indicator and status command returning
success, but not really.  The only sure way is to write data into every block
and see if the correct number of blocks are writable.

Command completion and inquiry status is obtained by having the 765 sample the
TRK00 floppy pin _exactly_ 13 ms after issuance of an inquiry or status command
(2 pulses) and checking the 765 internal state.  This system is not well-
documented in Irwin's OEM document so be cautious.  More information about
particulars can be had from the OEM document (a thicker book than the sales-
gimmick book that salesdrones typically mean when they promise 'documentation'.
Insist on the OEM book instead.  Also be cautious about the EPROM version that
can be found on the logic board next to the floppy cable connector.  Inquire
into the most-current revision, given that these drives are no longer in
production, as far as I know.
-- 
J.R. Stoner, DWMIT - asgard@plx.com - sun.com!plx!plxsun!asgard
From: edm@hpfcmdd.fc.hp.com (Ed Moore)
Date: Mon, 13 Apr 1992 15:58:06 GMT
Subject: Re: Dot Matrix Printer and Multi-Page Forms
Organization: HP Mechanical Design Division