5 using the scsi clock doubler, 6 using the scsi clock quadrupler, Using the scsi clock doubler – Avago Technologies LSI53C1010 User Manual
Page 227: Using the scsi clock quadrupler
Migrating Existing Software to Ultra, Ultra2, and Ultra3 SCSI
9-29
9.6.5 Using the SCSI Clock Doubler
The LSI53C875, LSI53C876, and LSI53C885 can double the frequency
of a 40–50 MHz SCSI clock, allowing the system to perform Ultra SCSI
transfers in systems that do not have 80 MHz clock input. This option is
user selectable with bit settings in the STEST1, STEST3, and SCNTL3
registers. At power on or reset, the doubler is disabled and powered
down. Follow these steps to use the clock doubler:
1.
Set the SCLK Doubler Enable bit (STEST1, bit 3).
2.
Wait 20
µ
s.
3.
Halt the SCSI clock by setting the Halt SCSI Clock bit (STEST3,
bit 5).
4.
Set the clock conversion factor using the SCF and CCF fields in the
SCNTL3 register.
5.
Set the SCLK Doubler Select bit (STEST1, bit 2).
6.
Clear the Halt SCSI Clock bit.
9.6.6 Using the SCSI Clock Quadrupler
The LSI53C895/895A/10XX can quadruple the frequency of a 40 MHz
SCSI clock, allowing the system to perform Ultra2 SCSI transfers. This
option is user selectable with bit settings in the STEST1, STEST3, and
SCNTL3 registers. At power on or reset, the quadrupler is disabled and
powered down. Use the following steps to use the clock quadrupler:
1.
Set the SCLK Quadrupler Enable bit (STEST1, bit 3).
2.
Poll bit 5 of the STEST4 register.
The LSI53C895 sets this bit as soon as it locks in the 160 MHz
frequency. The frequency lockup takes approximately
100 microseconds.
3.
Halt the SCSI clock by setting the Halt SCSI Clock bit (STEST3,
bit 5).
4.
Set the clock conversion factor using the SCF and CCF fields in the
SCNTL3 register.
5.
Set the SCLK Quadrupler Select bit (STEST1, bit 2).
6.
Clear the Halt SCSI Clock bit.