LSI LSI53C1000, Technical Manual

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2-42 Functional Description
2.2.15.1 SCSI Control Three (SCNTL3) Register, Bits [6:4] (SCF[2:0]) Description
The SCF[2:0] bits select the factor by which the frequency of SCLK is
divided before its presentation to the synchronous SCSI control logic.
The synchronous transfer speed is determined by the combination of the
divided clock and the setting of the XCLKS_ST, XCLKS_DT, XCLKH_ST,
and XCLKH_DT bits in the
SCSI Control Four (SCNTL4) register.
Table 2.6 provides the clock dividers available. Refer to Table 4.4 , " DT
Transfer Rates ," and Table 4.5, " Single Transition Transfer Rates,"
located in the SCSI Control Four (SCNTL4) register description, for a full
list of available synchronous transfer rates.
2.2.15.2 SCSI Control Four (SCNTL4) Register, Bits [3:0] Description
The following extra clock bits add an extra clock of setup or hold to a ST
or DT transaction.
Bit 3, XCLKH_DT (Extra Clock of Data Hold on DT transfer edge), adds
a clock of data hold to synchronous DT SCSI transfers on the DT edge.
This bit only impacts DT transfers as it only affects data hold to the DT
edge. Setting this bit reduces the synchronous transfer send rate but
does not reduce the rate at which the LSI53C1000 receives outbound
REQs, ACKs, or data.
Table 2.6 SCF Divisor Values
SCF2 SCF1 SCF0 SCLK Divisor
0 0 0 SCLK/3
0 0 1 SCLK/1
0 1 0 SCLK/1.5
0 1 1 SCLK/2
1 0 0 SCLK/3
1 0 1 SCLK/4
1 1 0 SCLK/6
1 1 1 SCLK/8