
SMSC DS – LPC47M14X 
Page 34 
Rev. 03/19/2001 
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 
RQM 
DIO 
NON 
DMA 
CMD 
BUSY 
Reserved
Reserved
DRV1 
BUSY 
DRV0 
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
Reserved, read ‘0’.  This part does not support non-DMA mode.
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. 
DATA REGISTER (FIFO) 
Address 3F5 READ/WRITE
All command parameter information, disk data and result status are transferred between the host processor and the 
floppy disk controller through the Data Register. 
Data transfers are governed by the RQM and DIO bits in the Main Status Register. 
The Data Register defaults to FIFO disabled mode after any form of reset.  This maintains PC/AT hardware 
compatibility.  The default values can be changed through the Configure command (enable full FIFO operation with 
threshold control).  The advantage of the FIFO is that it allows the system a larger DMA latency without causing a disk 
error.  Table 12 gives several examples of the delays with a FIFO.  
The data is based upon the following formula: 
Threshold # x 
1  
DATA 
RATE 
At the start of a command, the FIFO action is always disabled and command parameters must be sent based upon the 
RQM and DIO bit settings.  As the command execution phase is entered, the FIFO is cleared of any data to ensure that 
invalid data is not transferred. 
x 8 
- 1.5 
μ
s = 
DELAY