2-24
Functional Description
, and
registers. At
power-on or reset, the quadrupler is disabled and powered down. Follow
these steps to use the clock quadrupler:
1.
Set the SCLK Quadrupler Enable bit (
register, bit 3).
2.
Poll bit 5 of the
register. The LSI53C896
sets this bit as soon as it locks in the 160 MHz frequency. The
frequency lockin takes approximately 100 microseconds.
3.
Halt the SCSI clock by setting the Halt SCSI Clock bit (
register, bit 5).
4.
Set the clock conversion factor using the SCF and CCF fields in the
register.
5.
Set the SCLK Quadrupler Select bit (
, bit 2).
6.
Clear the Halt SCSI Clock bit.
2.2.6 Prefetching SCRIPTS Instructions
When enabled by setting the Prefetch Enable bit (bit 5) in the
register, the prefetch logic in the LSI53C896 fetches
8 Dwords of instruction. The prefetch logic automatically determines the
maximum burst size that it can perform, based on the burst length as
determined by the values in the
register. If the unit
cannot perform bursts of at least four Dwords, it disables itself. While the
chip is prefetching SCRIPTS instructions, it will use PCI cache
commands Memory Read Line, and Memory Read Multiple, if PCI
caching is enabled.
Note:
This feature is only useful when fetching SCRIPTS
instructions from main memory. Due to the short access
time of SCRIPTS RAM, prefetching is not necessary when
fetching instructions from this memory.
The LSI53C896 may flush the contents of the prefetch unit under certain
conditions to ensure that the chip always operates from the most current
version of the SCRIPTS instruction. When one of these conditions
applies, the contents of the prefetch unit are automatically flushed.
•
On every Memory Move instruction. The Memory Move instruction is
often used to place modified code directly into memory. To make
sure that the chip executes all recent modifications, the prefetch unit
*
Summary of Contents for LSI53C896
Page 6: ...vi Preface...
Page 16: ...xvi Contents...
Page 88: ...2 62 Functional Description...
Page 112: ...3 24 Signal Descriptions...
Page 306: ...6 38 Specifications This page intentionally left blank...
Page 310: ...6 42 Specifications This page intentionally left blank...
Page 338: ...6 70 Specifications Figure 6 40 LSI53C896 329 BGA Bottom View...
Page 340: ...6 72 Specifications...
Page 346: ...A 6 Register Summary...
Page 362: ...IX 12 Index...