
SMSC DS – LPC47M14X 
Page 32 
Rev. 03/19/2001 
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. 
7 
6 
5 
4 
S/W 
RESET 
DOWN 
COMP2 
RESET 
COND. 
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. 
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 250 Kbps. 
BIT 0 and 1  DATA RATE SELECT
These bits control the data rate of the floppy controller.  See Table 9 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 8 
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. 
3 
2 
1 
0 
POWER 
0 
PRE-
PRE-
COMP1 
0 
PRE-
COMP0 
0 
DRATE 
SEL1 
1 
DRATE 
SEL0 
0 
0 
0 
0 
0 
Table 8  –  Precompensation Delays 
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. 
Note:  
The DSR is Shadowed in the Floppy Data Rate Select Shadow Register, located at the offset 0x1F in the 
runtime register block Separator circuits will be turned off.  The controller will come out of  manual low power. 
PRECOMP 
432
PRECOMPENSATION 
DELAY (nsec) 
<2Mbps 
2Mbps 
111 
001 
010 
011 
100 
101 
110 
000 
0.00 
41.67 
83.34 
125.00 
166.67 
208.33 
250.00 
Default  
0 
20.8 
41.7 
62.5 
83.3 
104.2 
125 
Default 
Default: See Table 11