PC97338 datasheet(80/221 Pages) NSC

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Bits 3,2 - Logical Drive Control 1,0

(Enhanced Mode Only)

These read/write bits control logical drive ex-

change between drives 0 and 2. Drive 3 is never

exchanged for drive 2.

When four drives are configured, i.e., bit 4 of FER

is 1, logical drives are not exchanged.

00 - No logical drive exchange.

01 - Logical drives 0 and 1 are exchanged.

10 - Logical drives 0 and 2 are exchanged.

Software exchanges the physical floppy disk

control signals assigned to drives 0 and 2, i.e.,

DR0, DR23 and MTR0, as follows:

The internal signal that selects drive 2 uses

DR0; the internal signal that selects the motor

of drive 2 uses MTR0; and the DR0 internal

signal uses DR23.

11 - Reserved. Unpredictable results when 11 is

configured.

Bit 4 - Reserved

This bit is reserved.

Bit 5 - Valid Data

(Automatic Media Sense and Enhanced Modes)

This bit, together with bits 7,6, indicate what type

of media is currently in the active floppy disk drive,

as shown in Table 39.

TABLE 39. Media Type Bit Settings

The state of this bit reflects the value of either bit 1

or bit 0 of SCF2, i.e., the VLD1,0 bits. See bits 1,0

of SCF2 on page 58.

When two floppy disk drives are configured (bit 4

of FER is 0), this bit is the inverse of VLD0 (bit 0 of

SCF2) when drive 0 is accessed, and the inverse

of VLD1 (bit 1 of SCF2) when drive 1 is accessed.

Otherwise, bit 5 of TDR is 1.

0 - Automatic media sensing is enabled and there

is valid media ID sense data in bits 7 and 6 of

this register.

1 - Automatic media sensing is disabled.

Bit 6 - High Density

(Automatic Media Sense and Enhanced Modes)

When bit 5 is 0, this bit is used with bit 7 to indicate

the type of media currently in the active floppy disk

drive. If bit 5 is 1, it is invalid. See Table 39.

This bit reflects the value of the MSEN0 signal.

0 - If this bit is valid (bit 5 is 0), the floppy disk is

5.25 inch or 1.44 MB, depending on bit 7.

1 - If this bit is valid (bit 5 is 0), the floppy disk is

2.88 MB or 720 MB, depending on bit 7.

Bit 7 - Extra Density

(Automatic Media Sense and Enhanced Modes)

When bit 5 is 0, this bit is used with bit 6 to indicate

the type of media currently in the active floppy

drive. If bit 5 is 1, it is invalid. See Table 39.

This bit reflects the value of the MSEN1 signal.

0 - If this bit is valid (bit 5 is 0), the floppy disk is

5.25 inch or 2.88 MB, depending on bit 6.

1 - If this bit is valid (bit 5 is 0), the floppy disk is

1.44 MB or 720 MB, depending on bit 6.

3.3.6

Main Status Register (MSR),

Offset 100

This read-only register indicates the current status of

the Floppy Disk Controller (FDC), indicates when the

disk controller is ready to send or receive data

through the Data Register (FIFO) and controls the

flow of data to and from the Data Register (FIFO).

The MSR can be read at any time. It should be read

before each byte is transferred to or from the Data

lay is required when reading this register after a data

transfer.

The microprocessor can read the MSR immediately

after a hardware or software reset, or recovery from a

power down. The MSR contains a value of 00h, until

the FDC clock has stabilized and the internal registers

have been initialized.

When the FDC is ready to receive a new command, it

reports a value of 80h for the MSR to the micropro-

cessor. System software can poll the MSR until the

MSR is ready. The MSR must report an 80h value

(RQM set to 1) within 2.5 msec after reset or power

up.

Bit 7Bit 6Bit 5

Media Type

Invalid Data

1.2 MB (5.25")

010

2.88 MB

100

1.44 MB

720 KB

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