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From: thad@cup.portal.com (Thad P Floryan)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: Another disk/hardware question
Message-ID: <38518@cup.portal.com>
Date: 27 Jan 91 05:37:13 GMT
References: <11813@alice.att.com>
Organization: The Portal System (TM)
Lines: 61

wilber@alice.att.com (rew) in <11813@alice.att.com> writes:

	Could someone mail or post a brief description of what each of the
	signals on the 34 conductor disk cable does?  I want to have some
	notion of what I ought to be seeing when I do a recal.  This is
	probably worth posting, since other people are bound to have similar
	problems when they attack the motherboard in the quest for a bigger
	bucket of bits.

Ask and ye shall receive!  :-)

The Signals on the 34-pin cable are fairly standard, but note that OLDER drives
use pin 2 for write pre-comp (actually pre-distortion).  The pinnings for the
20-pin cable are from a Maxtor OEM manual which has some other options; the
only signals really used are the GNDs and the MFM Read/Write Data lines.

For the 34-wire daisy-chained cable:

	GND RTN		SIGNAL		Signal
	 PIN		 PIN		Name
	-------		-----		------------

	 1		 2		- Head Select 2^3
	 3		 4		- Head Select 2^2
	 5		 6		- Write Gate
	 7		 8		- Seek Complete
	 9		10		- Track 0
	11		12		- Write Fault
	13		14		- Head Select 2^0
	15		16		(reserved)
	17		18		- Head Select 2^1
	19		20		- Index
	21		22		- Ready
	23		24		- Step
	25		26		- Drive Select 1
	27		28		- Drive Select 2
	29		30		- Drive Select 3
	31		32		- Drive Select 4
	33		34		- Direction IN

And for the 20-pin radial cable:

	 2		 1		- Drive Selected
	 4		 3		- Remote Write Protect Option
	 6		 5		- Spindle Power Control Option
	 8		 7		(reserved)
	10		 9		(reserved)
	12		11		GND
			13		+ MFM Write Data
			14		- MFM Write Data
	16		15		GND
			17		+ MFM Read Data
			18		- MFM Read Data
	20		19		GND


One additional comment: I hope you've removed the disk's terminator resistor
pack on the first drive and kept the terminator pack on the LAST drive on the
34-wire daisy-chained cable.

Thad Floryan [ thad@cup.portal.com ]