FDC37B77X SMSC Corporation, FDC37B77X Datasheet - Page 25

• Manufacturer Part Number: FDC37B77X
• Description: ENHANCED SUPER I/O CONTROLLER WITH WAKE UP FEATURES
• Manufacturer: SMSC Corporation

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.
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.
several
examples
FIFO THRESHOLD
FIFO THRESHOLD
FIFO THRESHOLD
of
EXAMPLES
EXAMPLES
EXAMPLES
*The 2 Mbps data rate is only available if V
the
15 bytes
15 bytes
15 bytes
2 bytes
8 bytes
2 bytes
8 bytes
2 bytes
8 bytes
1 byte
1 byte
1 byte
delays
Table 14 gives
The default
Table 12 - FIFO Service Delay
with
1 x 4 s - 1.5 s = 2.5 s
2 x 4 s - 1.5 s = 6.5 s
8 x 4 s - 1.5 s = 30.5 s
15 x 4 s - 1.5 s = 58.5 s
1 x 8 s - 1.5 s = 6.5 s
2 x 8 s - 1.5 s = 14.5 s
8 x 8 s - 1.5 s = 62.5 s
15 x 8 s - 1.5 s = 118.5 s
1 x 16 s - 1.5 s = 14.5 s
2 x 16 s - 1.5 s = 30.5 s
8 x 16 s - 1.5 s = 126.5 s
15 x 16 s - 1.5 s = 238.5 s
MAXIMUM DELAY TO SERVICING AT 2
MAXIMUM DELAY TO SERVICING AT 1
MAXIMUM DELAY TO SERVICING AT
a
25
FIFO.
formula:
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.
An overrun or underrun will terminate the
current command and the transfer of data. Disk
writes will complete the current sector by
generating a 00 pattern and valid CRC. Reads
require the host to remove the remaining data
so that the result phase may be entered.
500 Kbps DATA RATE
Threshold # x
Mbps* DATA RATE
Mbps DATA RATE
The data is based upon the following
DATA RATE
CC
= 5V.
1
x 8 - 1.5 s = DELAY