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COMMON COMMAND SET AND DISK OPERATION
A-20
A
Pin 2 and Pin 34 Definition for High Density.
Pin 2 and Pin 34 Definition for Low Density.
3. Sectors/track is taken from the attach packet, byte offset $0C.
4. The number of bytes/sector is taken from the bytes per block
field in the attach packet, byte offset $1C.
5. The Number of cylinders is taken from the attach packet, byte
offset $08.
6. The write precompensation starting cylinder is taken from the
attach packet, byte offset $0A. The reduced write current
starting cylinder is also taken from the attach packet, byte
offset $0A (precompensation cylinder).
7. The drive step rate is specified in the attach packet, byte offset
$05 in units of 40 microseconds. This value is converted to 100
microsecond units before writing to page 5 of the mode select
command. A value of zero in the attach packet causes a
default of 6 milliseconds ($003C) to be written in page 5, offset
$0E.
8. The steps/cylinder field is either $01 or $02 depending on the
media and drive track descriptors in SCSI disk attributes
word of the attach packet, byte offset $10. If media TPI= drive
TPI, then $01 is used in the steps/cylinder field. If media
TPI= 1/2 drive TPI, then $02 is used in the steps/cylinder
field.
9. Pin34/pin2 descriptor byte. Pin 34 is selected as "Drive
Ready", and pin 2 is high/low density select. The level on this
signal is controlled by the flag in the attach packet, byte offset
$10, bit 4. If this bit is "1", 500k bits per second is selected and
pin 2 is low. This value is decoded below:
PIN 34 CONTROL
PIN 2 CONTROL
BIT
76543210COMMENTS
00010101Pin 34 = drive
ready, low true Bit
3 = 0) Pin 2 = 0
(high density)