DATA RATE SELECT REGISTER (DSR)
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
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
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
S/W POWER 0
PRE- PRE- PRE- DRATE DRATE
COMP2 COMP1 COMP0 SEL1 SEL0
BIT 0 and 1 DATA RATE SELECT
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 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.
BIT 5 UNDEFINED
Should be written as a logic "0".
BIT 6 LOW POWER
A logic "1" written to this bit will put the floppy controller
into Manual Low Power mode. The
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.
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.
Table 10 - Precompensation Delays
Default (See Table 14)