LSI 53C875A technical manual SCSIP20 Scsi Phase2624

Models: 53C875A

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register. These phase lines are latched when SREQ/ is asserted.

4.If the SCSI phase bits match the value stored in the SCSI SCSI Status One (SSTAT1) register, the LSI53C875A transfers the number of bytes specified in the DMA Byte Counter (DBC) register starting at the address pointed to by the DMA Next Address (DNAD) register. If the OpCode bit is cleared and a data transfer ends on an odd byte boundary, the LSI53C875A stores the last byte in the SCSI Wide Residue (SWIDE) register during a receive operation, or in the SCSI Output Data Latch (SODL) register during a send operation. This byte is combined with the first byte from the subsequent transfer so that a wide transfer can complete.

5.If the SCSI phase bits do not match the value stored in the SCSI Status One (SSTAT1) register, the LSI53C875A generates a phase mismatch interrupt and the instruction is not executed.

6.During a Message-Out phase, after the LSI53C875A has performed a select with Attention (or SATN/ is manually asserted with a Set ATN instruction), the LSI53C875A deasserts SATN/ during the final SREQ/SACK/ handshake.

7.When the LSI53C875A is performing a block move for Message-In phase, it does not deassert the SACK/ signal for the last SREQ/SACK/ handshake. Clear the SACK/ signal using the Clear SACK I/O instruction.

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

This 3-bit field defines the SCSI information transfer phase. When the LSI53C875A operates in Initiator mode, these bits are compared with the latched SCSI phase bits in the SCSI Status One (SSTAT1) register. When the LSI53C875A operates in Target mode, it asserts the phase defined in this field. Table 5.2 describes the possible combinations and the corresponding SCSI phase.

Block Move Instruction

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LSI 53C875A technical manual SCSIP20 Scsi Phase2624