DATA RATE SELECT REGISTER (DSR)
Microchannel applications. Other applications can set the
data rate in the DSR. The data rate of the floppy
controller is the most recent write of either the DSR or
Address 3F4 WRITE ONLY
This register is write only. It is used to program the data
rate, amount of write precompensation, power down
status, and software reset. The data rate is programmed
using the Configuration Control Register (CCR) not the
DSR, for PC/AT and PS/2 Model 30 and
CCR. The DSR is unaffected by a software reset. A
hardware reset will set the DSR to 02H, which
corresponds to the default precompensation setting and
250 kbps.
7
6
5
0
4
3
2
1
0
S/W
POWER
PRE-
PRE-
PRE-
DRATE DRATE
RESET DOWN
COMP2 COMP1 COMP0 SEL1
SEL0
RESET
COND.
0
0
0
0
0
0
1
0
BIT 0 and 1 DATA RATE SELECT
floppy controller clock and data separator circuits will be
turned off. The controller will come out of manual low
power mode after a software reset or access to the Data
Register or Main Status Register.
These bits control the data rate of the floppy controller.
See Table 13 for the settings corresponding to the
individual data rates. The data rate select bits are
unaffected by a software reset, and are set to 250 kbps
after a hardware reset.
BIT 7 SOFTWARE RESET
This active high bit has the same function as the DOR
RESET (DOR bit 2) except that this bit is self clearing.
BIT 2 through 4 PRECOMPENSATION SELECT
These three bits select the value of write
precompensation that will be applied to the WDATA
output signal. Table 12 shows the precompensation
values for the combination of these bits settings. Track 0
is the default starting track number to start
precompensation. this starting track number can be
changed by the configure command.
Table 10 - Precompensation Delays
PRECOMP
432
PRECOMPENSATION DELAY
111
001
010
011
100
101
110
000
0.00 ns-DISABLED
41.67 ns
83.34 ns
125.00 ns
166.67 ns
208.33 ns
BIT 5 UNDEFINED
Should be written as a logic "0".
250.00 ns
BIT 6 LOW POWER
A logic "1" written to this bit will put the floppy controller
into Manual Low Power mode. The
Default (See Table 14)
27
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