6 Apr
2013
6 Apr
'13
9:56 p.m.
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
7 Apr
7 Apr
3:13 a.m.
Jon,
First, lemme reassert my non-expert status on this.
However, my understanding of PE -- phase encoding as a raw signal -- is that a 0 is a low
to high transition(Thomas or reversed high to low for IEEE) against a fixed clock time.
Successive 0s have to be encoded taking the sign low to high, before going high to low
again. The system is to ignore those signals and simply count the transition at the
mid-point of the period. Setting the blocking aside, doesn't that mean you end up
with two transitions in a period for every zero. And if you write zero to every channel
you get a nice sine wave at the pre-amp, with the parity bit being the inverse signal (all
ones).
NZRI would of course be rather different. But for PE, this is my understand of the signal
inside a block. I believe that's the signal form you were thinking of.
-Colin
On 7 Apr 2013, at 05:56, Jon Elson <elson at pico-systems.com> wrote:
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
4229
days inactive
4229
days old
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