Write and Invalidate are each software enabled or disabled to allow the user full flexibility in using these commands. For more information on PCI cache mode operations, refer to Chapter 3, “PCI Functional Description.”

2.4.1 Load and Store Instructions

The LSI53C810A supports the Load and Store instruction type, which simplifies the movement of data between memory and the internal chip registers. It also enables the LSI53C810A to transfer bytes to addresses relative to the Data Structure Address (DSA) register. For more information on the Load and Store instructions, refer to

Chapter 6, “Instruction Set of the I/O Processor.”

2.4.2 3.3 V/5 V PCI Interface

The LSI53C810A can attach directly to a 3.3 V or a 5 V PCI interface, due to separate VDD pins for the PCI bus drivers. This allows the devices to be used on the universal board recommended by the PCI Special Interest Group.

2.4.3 Loopback Mode

The LSI53C810A loopback mode allows testing of both initiator and target functions and, in effect, lets the chip communicate with itself. When the Loopback Enable bit is set in the SCSI Test Two (STEST2) register, bit 4, the LSI53C810A allows control of all SCSI signals whether the chip is operating in the initiator or target mode. For more information on this mode of operation refer to the SCSI SCRIPTS Processors Programming Guide.

2.5 Parity Options

The LSI53C810A implements a flexible parity scheme that allows control of the parity sense, allows parity checking to be turned on or off, and has the ability to deliberately send a byte with bad parity over the SCSI bus to test parity error recovery procedures. Table 2.1 defines the bits that are involved in parity control and observation. Table 2.2 describes the parity control function of the Enable Parity Checking and Assert SCSI Even Parity bits in the SCSI Control Zero (SCNTL0) register. Table 2.3 describes the options available when a parity error occurs.

Parity Options

2-5

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LSI 53C810A technical manual Parity Options, Load and Store Instructions, 2 3.3 V/5 V PCI Interface, Loopback Mode