Configure Default Values:
EIS - No Implied Seeks
EFIFO - FIFO Disabled
POLL - Polling Enabled
FIFOTHR - FIFO Threshold Set to 1 Byte
PRETRK - Pre-Compensation Set to Track 0
EIS - Enable Implied Seek. When set to "1", the FDC will perform a Seek operation before executing a
read or write command. Defaults to no implied seek.
EFIFO - A "1" disables the FIFO (default). This means data transfers are asked for on a byte-by-byte
basis. Defaults to "1", FIFO disabled. The threshold defaults to "1".
POLL - Disable polling of the drives. Defaults to "0", polling enabled. When enabled, a single interrupt is
generated after a reset. No polling is performed while the drive head is loaded and the head unload delay
has not expired.
FIFOTHR - The FIFO threshold in the execution phase of read or write commands. This is programmable
from 1 to 16 bytes. Defaults to one byte. A "00" selects one byte; "0F" selects 16 bytes.
PRETRK - Pre-Compensation Start Track Number. Programmable from track 0 to 255. Defaults to track
0. A "00" selects track 0; "FF" selects track 255.
Version
The Version command checks to see if the controller is an enhanced type or the older type (765A). A
value of 90 H is returned as the result byte.
Relative Seek
The command is coded the same as for Seek, except for the MSB of the first byte and the DIR bit.
DIR Head Step Direction Control
RCN Relative Cylinder Number that determines how many tracks to step the head in or out from the
current track number.
66