A |
COMMON COMMAND SET AND DISK OPERATION
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 2 and Pin 34 Definition for High Density.
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| PIN 34 CONTROL |
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| PIN 2 CONTROL |
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BIT | 7 |
| 6 | 5 |
| 4 | 3 |
| 2 | 1 |
| 0 | COMMENTS | |
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| 0 |
| 0 | 0 |
| 1 | 0 |
| 1 | 0 |
| 1 | Pin 34 = drive | |
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| ready, low true Bit | |
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| 3 = 0) Pin 2 = 0 | |
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| (high density) | |
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