
IT8673F
2
Table 11-21. SRT Values
Parameter
0
1 Mbps
8
500 Kbps
16
300 Kbps
26.7
250 Kbps
32
1
7.5
15
25
30
…
…
…
…
…
E
1
2
3.33
4
F
0.5
1
1.67
2
Table 11-22. HLT Values
Parameter
00
1 Mbps
128
500 Kbps
256
300 Kbps
426
250 Kbps
512
01
1
2
3.33
4
02
2
4
6.7
8
…
…
…
…
…
7E
126
252
420
504
7F
127
254
423
508
11.4.12.12 PERPENDICULAR MODE
The PERPENDICULAR MODE command is used to support the unique READ/WRITE/FORMAT
commands of Perpendicular Recording disk drives (4 Mbytes unformatted capacity). This command
configures each of the four logical drives as a perpendicular or conventional disk drive via the DC3-DC0
bits, or with the GAP and WG control bits. Perpendicular Recording drives operate in “Extra High Density”
mode at 1Mbps, and are downward compatible with 1.44 Mbyte and 720 kbyte drives at 500 Kbps (High
Density) and 250 Kbps (Double Density) respectively. This command should be issued during the
initialization of the floppy disk controller. Then, when a drive is accessed for a FORMAT A TRACK or
WRITE DATA command, the controller adjusts the format or Write Data parameters based on the data rate.
If WG and GAP are used (not set to 00), the operation of the FDC is based on the values of GAP and WG.
If WG and GAP are set to 00, setting DCn to 1 will set drive n to Perpendicular mode. DC3-DC0 are
unaffected by a software reset, but WG and GAP are both cleared to 0 after a software reset.
Table 11-23. Effects of GAP and WG on FORMAT A TRACK and WRITE DATA Commands
GAP
WG
Mode
Length of GAP2
FORMAT FIELD
22 bytes
Portion of GAP2 Re-Written by WRITE
DATA Command
0 bytes
0
0
Conventional
0
1
Perpendicular
(500 Kbps)
22 bytes
19 bytes
1
0
Reserved
(Conventional)
22 bytes
0 bytes
1
1
Perpendicular
(1 Mbps)
41 bytes
38 bytes