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
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
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 250 kbps.
data
rate
is
programmed
using
the
Configuration Control Register (CCR) not the
DSR, for PC/AT and PS/2 Model 30 and
7
6
5
0
4
3
2
1
0
S/W POWER
RESET DOWN
PRE-
PRE-
PRE- DRATE DRATE
COMP2 COMP1 COMP0 SEL1
SEL0
RESET
COND.
0
0
0
0
0
0
1
0
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 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 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
SELECT
2
through
4
PRECOMPENSATION
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
Default (See Table 14)
BIT 6 LOW POWER
A logic "1" written to this bit will put the floppy
controller into Manual Low Power mode. The
27
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