HTHHandshake-to-Handshake Timer Expired0

The handshake-to-handshake timer is expired. The time measured is the SCSI Request-to-Request (target) or Acknowledge-to-Acknowledge (initiator) period. See the description of the SCSI Timer Zero (STIME0) register, bits [7:4], for more information on the handshake- to-handshake timer.

Register: 0x42

SCSI Interrupt Status Zero (SIST0)

Read Only

7

6

5

4

3

2

1

0

M/A

CMP

SEL

RSL

SGE

UDC

RST

PAR

 

 

 

 

 

 

 

 

0

0

0

0

0

0

0

0

 

 

 

 

 

 

 

 

Reading the SIST0 register returns the status of the various interrupt conditions, whether they are enabled in the SCSI Interrupt Enable Zero (SIEN0) register or not. Each bit set indicates occurrence of the corresponding condition. Reading the SIST0 clears the interrupt status.

Reading this register clears any bits that are set at the time the register is read, but does not necessarily clear the register because additional interrupts may be pending (the LSI53C875A stacks interrupts). SCSI interrupt conditions are individually masked through the SCSI Interrupt Enable Zero (SIEN0) register.

When performing consecutive 8-bit reads of the DMA Status (DSTAT), SCSI Interrupt Status Zero (SIST0), and SCSI Interrupt Status One (SIST1) registers (in any order), insert a delay equivalent to 12 CLK periods between the reads to ensure the interrupts clear properly. Also, if reading the registers when both the Interrupt Status Zero (ISTAT0) SIP and DIP bits may not be set, read the SIST0 and SIST1 registers before the DSTAT register to avoid missing a SCSI interrupt. For more information on interrupts, refer to Chapter 2, “Functional Description.”

M/A

Initiator Mode: Phase Mismatch; Target Mode:

 

 

SATN/ Active

7

In the initiator mode, this bit is set if the SCSI phase asserted by the target does not match the instruction. The phase is sampled when SREQ/ is asserted by the

4-76Registers

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LSI 53C875A technical manual HTHHandshake-to-Handshake Timer Expired0, Scsi Interrupt Status Zero SIST0 Read Only