Table 9 - DRVDEN Mapping
DT1
0
DT0
0
DRVDEN1 (1)
DRVDEN0 (1)
DRIVE TYPE
4/2/1 MB 3.5"
DRATE0
DENSEL
2/1 MB 5.25" FDDS
2/1.6/1 MB 3.5" (3-MODE)
1
0
1
0
1
1
DRATE0
DRATE0
DRATE1
DRATE1
nDENSEL
DRATE0
PS/2
Table 10 - Default Precompensation Delays
PRECOMPENSATION
DATA RATE
DELAYS
2 Mbps
1 Mbps
500 Kbps
300 Kbps
250 Kbps
20.8 ns
41.67 ns
125 ns
125 ns
125 ns
MAIN STATUS REGISTER
Address 3F4 READ ONLY
The Main Status Register is a read-only register and indicates the status of the disk controller. The Main Status Register
can be read at any time. The MSR indicates when the disk controller is ready to receive data via the Data Register. It
should be read before each byte transferring to or from the data register except in DMA mode. No delay is required
when reading the MSR after a data transfer.
7
6
5
4
3
2
1
0
NON
DMA
CMD
DRV1
DRV0
BUSY
RQM
DIO
BUSY Reserved Reserved BUSY
BIT 0 - 1 DRV x BUSY
These bits are set to 1s when a drive is in the seek portion of a command, including implied and overlapped seeks and
recalibrates.
BIT 4 COMMAND BUSY
This bit is set to a 1 when a command is in progress. This bit will go active after the command byte has been accepted
and goes inactive at the end of the results phase. If there is no result phase (Seek, Recalibrate commands), this bit is
returned to a 0 after the last command byte.
BIT 5 NON-DMA
This mode is selected in the SPECIFY command and will be set to a 1 during the execution phase of a command. This
is for polled data transfers and helps differentiate between the data transfer phase and the reading of result bytes.
BIT 6 DIO
Indicates the direction of a data transfer once a RQM is set. A 1 indicates a read and a 0 indicates a write is required.
BIT 7 RQM
Indicates that the host can transfer data if set to a 1. No access is permitted if set to a 0.
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