82077AA Datasheet, PDF (32/62 Pages) Intel Corporation – CHMOS SINGLE-CHIP FLOPPY DISK CONTROLLER

82077AA
Table 5-10 Drive Control Delays (ms)
HUT
SRT
1M 500K 300K 250K 1M 500K 300K 250K
0 128 256 426 512 8 0 16 26 7 32
1 8 16 26 7 32 7 5 15 25 30
E 112 224 373 448 1 0 2 3 33 4
F 120 240 400 480 0 5 1 1 67 2
HLT
1M
500K
300K
250K
00
128
256
426
512
01
1
2
33
4
02
2
4
67
8
7F
126
252
420
504
7F
127
254
423
508
The choice of DMA or NON-DMA operations is
made by the ND bit When this bit is ‘‘1’’ the NON-
DMA mode is selected and when ND is ‘‘0’’ the
DMA mode is selected In DMA mode data transfers
are signalled by the DRQ pin Non-DMA mode uses
the RQM bit and the INT pin to signal data transfers
5 2 7 CONFIGURE
Issued to select the special features of the
82077AA A CONFIGURE command need not be is-
sued if the default values of the 82077AA meet the
system requirements
CONFIGURE DEFAULT VALUES
EIS
EFIFO
POLL
FIFOTHR
PRETRK
No Implied Seeks
FIFO Disabled
Polling Enabled
FIFO Threshold Set to 1 Byte
Pre-Compensation Set to Track 0
EIS Enable implied seek When set to ‘‘1’’ the
82077AA will perform a SEEK operation before exe-
cuting a read or write command Defaults to no im-
plied seek
EFIFO A ‘‘1’’ puts the FIFO into the 8272A com-
patible mode where the FIFO is disabled This
means data transfers are asked for on a byte by byte
basis Defaults to ‘‘1’’ FIFO disabled The threshold
defaults to one
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 program-
mable 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 255
5 2 8 VERSION
The VERSION command checks to see if the con-
troller is an enhanced type or the older type (8272A
765A) A value of 90 H is returned as the result byte
defining an enhanced FDD controller is in use No
interrupts are generated
5 2 9 RELATIVE SEEK
The command is coded the same as for SEEK ex-
cept for the MSB of the first byte and the DIR bit
DIR Head Step Direction Control
DIR
Action
0
Step Head Out
1
Step Head In
RCN Relative Cylinder Number that determines
how many tracks to step the head in or out
from the current track number
The RELATIVE SEEK command differs from the
SEEK command in that it steps the head the abso-
lute number of tracks specified in the command in-
stead of making a comparison against an internal
register The SEEK command is good for drives that
support a maximum of 256 tracks RELATIVE
SEEKs cannot be overlapped with other RELATIVE
SEEKs Only one RELATIVE SEEK can be active at
a time Bit 4 of Status Register 0 (EC) will be set if
RELATIVE SEEK attempts to step outward beyond
Track 0
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