Date: Sun, 7 Apr 2013 00:10:24 +0100
From: Colin Eby <colineby at isallthat.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Subject: Re: 9-track alignment (skew) tapes for R/W-head adjustment
Message-ID: <975726A4-6B0E-4EE6-BB5E-B518CAA638B6 at isallthat.com>
Content-Type: text/plain; charset=windows-1252
If you don't have a alignment tape, you might try simply creating a
/dev/zero tape from a known good drive.
No, this won't work. It will only have transitions in the parity
channel, all other
channels (0-7) will have no transitions at all except at the end of the
block (CRC
and LRCC). Writing all 1's will have transitions on all data channels AND
the parity channel (to get odd parity on each byte).
Drives made for alignment with a scope have a resistor summing network that
sums the bit detector on each channel. With bad alignment you see a wave
with lots of stairsteps up and down the side. With correct alignment, it
becomes almost a perfect square wave, with at most one narrow step on
the sides.
Jon
Jon