TABLE 19 - STATUS REGISTER 3
NAME DESCRIPTION
BIT NO.
SYMBOL
7
6
Unused. This bit is always "0".
WP
Write
Indicates the status of the WP pin.
Protected
5
4
Unused. This bit is always "1".
Indicates the status of the TRK0 pin.
Unused. This bit is always "1".
T0
Track 0
3
2
HD
Head Address Indicates the status of the HDSEL pin.
1,0
DS1,0
Drive Select
Indicates the status of the DS1, DS0 pins.
Both will reset the FDC core, which affects drive
status information and the FIFO circuits. The DSR
reset clears itself automatically while the DOR
reset requires the host to manually clear it. DOR
reset has precedence over the DSR reset. The
DOR reset is set automatically upon a pin reset.
The user must manually clear this reset bit in the
DOR to exit the reset state.
RESET
There are three sources of system reset on the
FDC: the RESET pin of the FDC, a reset
generated via a bit in the DOR, and a reset
generated via a bit in the DSR. At power on, a
Power On Reset initializes the FDC. All resets
take the FDC out of the power down state.
All operations are terminated upon a RESET, and
the FDC enters an idle state. A reset while a disk
write is in progress will corrupt the data and CRC.
MODES OF OPERATION
The FDC has three modes of operation, PC/AT
mode, PS/2 mode and Model 30 mode. These
are determined by the state of the IDENT and
MFM bits 3 and 2 respectively of LD8CRF0.
On exiting the reset state, various internal
registers are cleared, including the Configure
command information, and the FDC waits for a
new command. Drive polling will start unless
disabled by a new Configure command.
PC/AT mode - (IDENT high, MFM a "don't care")
The PC/AT register set is enabled, the DMA
enable bit of the DOR becomes valid (FINTR and
DRQ can be hi Z), and TC and DENSEL become
active high signals.
RESET Pin (Hardware Reset)
The RESET pin is a global reset and clears all
registers except those programmed by the Specify
command. The DOR reset bit is enabled and
must be cleared by the host to exit the reset state.
PS/2 mode - (IDENT low, MFM high)
This mode supports the PS/2 models 50/60/80
configuration and register set. The DMA bit of the
DOR becomes a "don't care", (FINTR and DRQ
are always valid), TC and DENSEL become active
low.
DOR Reset vs. DSR Reset (Software Reset)
These two resets are functionally the same.
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