SCSI Functional Description
2-49
•
The LSI53C896 attempts to clean up any outstanding synchronous
offset before halting.
•
In the case of Transfer Control Instructions, once instruction
execution begins it continues to completion before halting.
•
If the instruction is a JUMP/CALL WHEN/IF <phase>, the
is updated to the transfer address before
halting.
•
All other instructions may halt before completion.
2.2.16.7 Sample Interrupt Service Routine
The following is a sample of an interrupt service routine for the
LSI53C896. It can be repeated if polling is used, or should be called
when the INTA/ (or INTB/) pin is asserted if hardware interrupts are used.
1.
Read
Interrupt Status Zero (ISTAT0)
2.
If the INTF bit is set, it must be written to a one to clear this status.
3.
If only the SIP bit is set, read
SCSI Interrupt Status Zero (SIST0)
and
SCSI Interrupt Status One (SIST1)
to clear the SCSI interrupt
condition and get the SCSI interrupt status. The bits in the SIST0
and SIST1 tell which SCSI interrupts occurred and determine what
action is required to service the interrupts.
4.
If only the DIP bit is set, read
to clear the
interrupt condition and get the DMA interrupt status. The bits in
DSTAT tell which DMA interrupts occurred and determine what action
is required to service the interrupts.
5.
If both the SIP and DIP bits are set, read
,
SCSI Interrupt Status One (SIST1)
, and
to clear the SCSI and DMA interrupt condition and get the
interrupt status. If using 8-bit reads of the SIST0, SIST1, and DSTAT
registers to clear interrupts, insert a 12 clock delay between the
consecutive reads to ensure that the interrupts clear properly. Both
the SCSI and DMA interrupt conditions should be handled before
leaving the Interrupt Service Routine. It is recommended that the
DMA interrupt is serviced before the SCSI interrupt, because a
serious DMA interrupt condition could influence how the SCSI
interrupt is acted upon.
*
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...