FDC37C669-MT datasheet(27/162 Pages) MICROCHIP

27 / 162 page

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

250 kbps.

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

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

the

default

starting

track

number

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

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

S/W

RESET

POWER

DOWN

PRE-

COMP2

PRE-

COMP1

PRE-

COMP0

DRATE

SEL1

DRATE

SEL0

RESET

COND.

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

250.00 ns

Default (See Table 14)

FDC37C669-MT Datasheet(PDF) 27 Page - Microchip Technology

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