PC87338 Datasheet, PDF (80/221 Pages) National Semiconductor (TI) – ACPI 1.0 and PC98/99 Compliant SuperI/O

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
Bit 7
X
0
0
1
1
Bit 6
X
0
1
0
1
Bit 5
1
0
0
0
0
Media Type
Invalid Data
1.2 MB (5.25")
2.88 MB
1.44 MB
720 KB
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
Register (FIFO) except during a DMA transfer. No de-
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.
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