Avago Technologies LSI53C825AE - Manual (Page 120)

4-32 Registers
The LSI53C825A is connected to a hard disk which can
transfer data at 10 Mbytes/s synchronously. The
LSI53C825A SCLK is running at 40 MHz. The
synchronous transfer period (SXFERP) is found as
follows:
SXFERP = Period/SSCP + ExtCC
Period = 1
÷
Frequency = 1
÷
10 Mbytes/s = 100 ns
SSCP = 1
÷
SSCF = 1
÷
40 MHz = 25 ns
(This SCSI synchronous core clock is determined in
SCSI Control Three (SCNTL3) , bits [6:4], ExtCC = 1 if
SCSI Control One (SCNTL1) , bit 7 is asserted and the
LSI53C825A is sending data. ExtCC = 0 if the
LSI53C825A is receiving data.)
SXFERP = 100
÷
25 = 4
Where
SXFERP Synchronous transfer period
SSCP SCSI synchronous core period
SSCF SCSI synchronous core frequency
ExtCC Extra clock cycle of data setup