PC87303VUL Datasheet, PDF (30/114 Pages) National Semiconductor (TI) – PC87303VUL SuperI/OTM Sidewinder Lite Floppy Disk Controller, Keyboard Controller, Real-Time Clock, Dual UARTs, IEEE 1284 Parallel Port, and IDE Inter

3 0 FDC Register Description (Continued)
TABLE 3-3 TDR Operation Modes
Mode
FCR ASC
Bit
D7 D6
D5
D4
Bit 0 Bit 2
Compatible PC-AT TDR 1
Automatic Media Sense 0
DESC
X
X
X
X
0
RESET
COND ^{N A N A}
NA
NA
VALID
DESC ED HD
X
DATA
0
RESET _{N A N A}
NA
NA
COND
Enhanced
0
DESC ED HD DRID1 DRID0
or
1
1
RESET
COND ^{N A N A}
NA
NA
D3
X
NA
X
NA
SWP1
0
D2
X
NA
X
NA
SWP0
0
D1
TAPE
SEL 1
0
TAPE
SEL 1
0
TAPE
SEL 1
0
D0
TAPE
SEL 0
0
TAPE
SEL 0
0
TAPE
SEL 0
0
D7
D6
D5
D4 5
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 MSEN0 DRATE0 pin value See Ta-
ble 3-4 for details regarding bits 5–7
Note Bits 6 and 7 of TDR are undefined when DRID0 1 pins are
configured as DRATE0 1
Valid Data (For Automatic Media Sense mode)
The state of bit 5 is determined by the state of the
VLD0 1 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
Drive ID0 1 (For Enhanced mode)
Bits 4 and 5 are read only bits which hold DRID0 1
pins values
TABLE 3-4 Media ID Bits Functions
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
5 25
2 88M
1 44M
720k
D3 2
D1 0
Bits 3 and 2 are read write 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
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
0
0
1
1
TAPESEL0
0
1
0
1
Drive
Selected
None
1
2
3
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