37C957FR Datasheet, PDF (45/328 Pages) SMSC Corporation – ULTRA I/O CONTROLLER FOR PORTABLE APPLICATIONS

Threshold # x [8/DATA RATE] - 1.5ms = Delay
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.
Table 19 - FIFO Service Delay
FIFO THRESHOLD
MAXIMUM DELAY TO SERVICING
EXAMPLES
AT 2 Mbps* DATA RATE
1 byte
1 x 4 ms - 1.5 ms = 2.5 ms
2 bytes
2 x 4 ms - 1.5 ms = 6.5 ms
8 bytes
8 x 4 ms - 1.5 ms = 30.5 ms
15 bytes
15 x 4 ms - 1.5 ms = 58.5 ms
FIFO THRESHOLD
EXAMPLES
1 byte
2 bytes
8 bytes
15 bytes
MAXIMUM DELAY TO SERVICING
AT 1 Mbps DATA RATE
1 x 8 ms - 1.5 ms = 6.5 ms
2 x 8 ms - 1.5 ms = 14.5 ms
8 x 8 ms - 1.5 ms = 62.5 ms
15 x 8 ms - 1.5 ms = 118.5 ms
FIFO THRESHOLD
MAXIMUM DELAY TO SERVICING
EXAMPLES
AT 500 Kbps DATA RATE
1 byte
1 x 16 ms - 1.5 ms = 14.5 ms
2 bytes
2 x 16 ms - 1.5 ms = 30.5 ms
8 bytes
8 x 16 ms - 1.5 ms = 126.5 ms
15 bytes
15 x 16 ms - 1.5 ms = 238.5 ms
The 2 Mbps data rate is only available if VCC = 5V nominal.
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