4-32 Registers
(This SCSI synchronous core clock is determined in
SCNTL3 bits [6:4], ExtCC = 1 if SCNTL1 bit 7 is asserted
and the LSI53C875A is sending data. ExtCC = 0 if the
LSI53C875A is receiving data.)
SXFERP = 100 ÷25 = 4
Where:
Tabl e 4.3 shows examples of synchronous transfer periods and rates for
SCSI-1.
SXFERP Synchronous transferperiod.
SSCP SCSI synchronous core period.
SSCF SCSI synchronous core frequency.
ExtCC Extra clock cycle of data setup.
Table 4.3 Examples of Synchronous TransferPeriods and Rates
for SCSI-1
CLK (MHz)
SCSICLK ÷
SCNTL3
Bits [6:4]
XFERP
(SXFER
Bits [7:5])
Synch.
Transfer
Period (ns)
Synch.
TransferRate
(Mbytes/s)
66.67 3 4 180 5.55
66.67 3 5 225 4.44
50 2 4 160 6.25
50 2 5 200 5
40 2 4 200 5
37.50 1.5 4 160 6.25
33.33 1.5 4 180 5.55
25 1 4 160 6.25
20 1 4 200 5
16.67 1 4 240 4.17