PC87303 datasheet(30/114 Pages) NSC

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30 FDC Register Description (Continued)

TABLE 3-3 TDR Operation Modes

Mode

FCR

ASC

Bit

Bit 0

Bit 2

Compatible PC-AT TDR

DESC

TAPE

SEL 1

SEL 0

RESET

COND

Automatic Media Sense

DESC

VALID

TAPE

DATA

SEL 1

SEL 0

RESET

COND

Enhanced

DESC

DRID1

DRID0

SWP1

SWP0

TAPE

SEL 1

SEL 0

RESET

COND

Extra Density

When bit 5 is 0 this media id bit is

used with bit 6 to indicate the type of media current-

ly in the active floppy drive If bit 5 is 1 it is invalid

This bit holds MSEN1 pin value See Table 3-4 for

details regarding bits 5 – 7

High Density

When bit 5 is 0 this media id bit is

used with bit 7 to indicate the type of media current-

ly in the active floppy drive If bit 5 is 1 it is invalid

This bit holds MSEN0DRATE0 pin value See Ta-

ble 3-4 for details regarding bits 5 – 7

Note

Bits 6 and 7 of TDR are undefined when DRID01 pins are

configured as DRATE01

Valid Data

(For Automatic Media Sense mode)

The state of bit 5 is determined by the state of the

VLD01 pins during reset If this bit is 0 there is valid

media id sense data in bits 7 and 6 of this register

Bit 5 holds VLD0 when drive 0 is accessed and

media sense is configurfed It holds VLD1 when

drive 1 is accessed and media sense is configured

Otherwise it is set to 1 to indicate that media infor-

mation is not available See Table 3-4 for details

regarding bits 5 – 7

D4 5

Drive ID01

(For Enhanced mode)

Bits 4 and 5 are read only bits which hold DRID01

pins values

TABLE 3-4 Media ID Bits Functions

Bit 7

Bit 6

Bit 5

Media Type

Invalid Data

525

288M

144M

720k

D3 2

Bits 3 and 2 are readwrite bits that control bits con-

trol logical drive exchange

When working with four drives encoding (bit 4 of

FER is 1) the logical drive exchange is not per-

formed

00 No logical drive exchange

01 logical drive exchange between drives 0 and 1

as done by bit 4 of FCR

10 Logical drive exchange between drives 0 and 2

This bit allows software to exchange the physi-

cal floppy-disk control signals assigned to drive

0 and 2 The DR0 DR23 and MTR0 pins func-

tion is exchanged as follows

DR2 internal signal to DR0 pin

MTR2 internal signal to MTR0 pin

DR0 internal signal to DR23 pin

Note

Drive 3 is not exchanged together wth drive 2

11 Reserved

Unpredictable results when 11 is

configured

D1 0

Tape Select 1 0

These bits assign a logical drive

number to a tape drive Drive 0 is not available as a

tape drive and is reserved as the floppy disk boot

drive See Table 3-5 for the tape drive assignment

values

TABLE 3-5 Tape Drive Assignment Values

TAPESEL1

TAPESEL0

Drive

Selected

None

PC87303 Datasheet(PDF) 30 Page - National Semiconductor (TI)

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