During a Transfer Control instruction, the Compare Data (bit 18) and Compare Phase (bit 17) bits are set in the DMA Byte Counter (DBC) register while the LSI53C875A is in target mode.

During a Transfer Control instruction, the Carry Test bit (bit 21) is set and either the Compare Data (bit 18) or Compare Phase (bit 17) bit is set.

A Transfer Control instruction is executed with the reserved bit 22 set.

A Transfer Control instruction is executed with the Wait for Valid phase bit (bit 16) set while the chip is in target mode.

A Load/Store instruction is issued with the

memory address mapped to the operating registers of the chip, not including ROM or RAM.

A Load/Store instruction is issued when the register address is not aligned with the memory address.

A Load/Store instruction is issued with bit 5 in the DMA Command (DCMD) register cleared or bits 3 or 2 set.

A Load/Store instruction when the count value in the DMA Byte Counter (DBC) register is not set at 1 to 4.

A Load/Store instruction attempts to cross a Dword boundary.

A Memory Move instruction is executed with one of the reserved bits in the DMA Command (DCMD) register set.

A Memory Move instruction is executed with the source and destination addresses not aligned.

A 64-bit Table Indirect Block Move instruction is executed with a selector index value greater than 0x16.

If the Select with ATN/ bit 24 is set for any I/O instruction other than a Select instruction.

SCSI Registers

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LSI 53C875A technical manual Scsi Registers