GM82C803CN Datasheet, PDF (34/84 Pages) List of Unclassifed Manufacturers – 2.88 MB FDC/ Dual UARTs with FIFO/PIO(EPP/ ECP)/ IDE Interface/ S-IR/ PnP

GM82C803CN
Data Rate Select Register (DSR)
This write-only register is used to program the timings of the drive control signals. To ensure that drive timings are not
violated when changing data rates, choose a drive timing such that the fastest data rate will not violate the timing. The
data rate is programmed via the Control Register, not the DSR. Other application can set the data rate in the DSR. The
data rate of the floppy controller is determined by the most recent write to either the DSR or CR. The DSR is
unaffected by a software reset. A hardware reset will set the DSR to 02H, which correspond to the default
precompensation setting and 250 Kbps.
D7 Software Reset : This bit behaves the same as Operations Register RESET except that this reset is self
clearing.
D6 _{Power Down : This bit will put the controller into the Manual Low Power mode when set to one.}
D5 Undefined. Should be set to zero.
D4-2
Precompensation Select : These three bits select the amount of write precompensation which the floppy
controller will use on the WDATA disk interface output. Table 4-15 shows the amount of precompensation
used for each bit pattern. In most cases, the default values (Table 4-16) can be used ; however, alternate values
can be chosen for specific types of drives and media. Track 0 is the default starting track number can be
changed in the Configure command.
Table 4-15. Write Precompensation Delays Table 4-16. Default Precompensation Delays
Precomp.
432
111
001
010
011
100
101
110
000
Precompensation Delays
0.0 ns Disabled
41.7 ns
83.3 ns
125.0 ns
166.7 ns
208.3 ns
250.0 ns
Default
Data Rate
1 Mbps
500 Kbps
300 Kbps
250 Kbps
Precompensation Delays
41.7 ns
125.0 ns
125.0 ns
125.0 ns
D1-0 Data Rate Select 1,0 : These bits determine the data rate for the floppy controller. See Table 4-17 for the
corresponding data rate for each value of D1, D0. The data rate select bits are unaffected by a software reset,
and are set to 250 Kbps after a hardware reset.
Table 4-17. Data Rates
Data Rate Select
10
Data Rate
MFM
FM
11
00
01
10
1 Mbps
500 Kbps
300 Kbps
250 Kbps
Illegal
250 Kbps
150 Kbps
125 Kbps
Control Register (CR)
This register sets the data rate and is write only. This is not affect by a software reset, and is set to 250 Kbps after a
hardware reset. The data rate of the floppy disk controller is determined by the last write to either this register or DSR.
D7-2 Reserved : Should be set to 0.
D1-0 Data Rate Select 1,0 : See Table 4-17 for the appropriate values.