If the comparisons are false, the LSI53C875A fetches the next instruction from the address pointed to by the DSP register and the instruction pointer is not modified.

Interrupt Instruction

The LSI53C875A can do a true/false comparison of the ALU carry bit, or compare the phase and/or data as defined by the Phase Compare, Data Compare, and True/False bit fields.

If the comparisons are true, the LSI53C875A generates an interrupt by asserting the IRQ/ signal.

The 32-bit address field stored in the DMA SCRIPTS Pointer Save (DSPS) register can contain a unique interrupt service vector. When servicing the interrupt, this unique status code allows the Interrupt Service Routine to quickly identify the point at which the interrupt occurred.

The LSI53C875A halts and the DMA SCRIPTS Pointer (DSP) register must be written to before starting any further operation.

Interrupt-on-the-Fly Instruction

The LSI53C875A can do a true/false comparison of the ALU carry bit or compare the phase and/or data as defined by the Phase Compare, Data Compare, and True/False bit fields. If the comparisons are true, and the Interrupt-on-the-Fly bit (Interrupt Status One (ISTAT1) bit 2) is set, the LSI53C875A asserts the Interrupt-on-the- Fly bit.

SCSIP[2:0] SCSI Phase[26:24]

This 3-bit field corresponds to the three SCSI bus phase signals that are compared with the phase lines latched when SREQ/ is asserted. Comparisons can be performed to determine the SCSI phase actually being driven on the SCSI bus. Table 5.5 describes the possible combinations and their corresponding SCSI phase. These bits are only valid when the LSI53C875A is operating in Initiator mode. Clear these bits when the LSI53C875A is operating in Target mode.

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SCSI SCRIPTS Instruction Set

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LSI 53C875A technical manual Interrupt Instruction, Interrupt-on-the-Fly Instruction