ZMOD

High Impedance Mode

6

 

Setting this bit causes the LSI53C810A to place all output

 

and bidirectional pins into a high impedance state. In

 

 

order to read data out of the LSI53C810A, clear this bit.

 

This bit is intended for board-level testing only. Do not set

 

this bit during normal system operation.

 

ZSD

SCSI Data High Impedance

5

 

Setting this bit causes the LSI53C810A to place the SCSI

 

data bus SD[7:0] and the parity line (SDP) in a high

 

 

impedance state. In order to transfer data on the SCSI

 

 

bus, clear this bit.

 

SRTM

Shadow Register Test Mode

4

 

Setting this bit allows access to the shadow registers

 

 

used by Memory-to-Memory Move operations. When this

 

bit is set, register accesses to the Temporary (TEMP) and

 

Data Structure Address (DSA) registers are directed to

 

 

the shadow copies STEMP (Shadow TEMP) and SDSA

 

(Shadow DSA). The registers are shadowed to prevent

 

 

them from being overwritten during a Memory-to-Memory

 

Move operation. The DSA and Temporary (TEMP)

 

 

registers contain the base address used for table indirect

 

calculations, and the address pointer for a call or return

 

instruction, respectively. This bit is intended for

 

 

manufacturing diagnostics only and should not be set

 

 

during normal operations.

 

MPEE Master Parity Error Enable3

Setting this bit enables parity checking during master data phases. A parity error during a bus master read is detected by the LSI53C810A. A parity error during a bus master write is detected by the target, and the LSI53C810A is informed of the error by the PERR/ pin being asserted by the target. When this bit is cleared, the LSI53C810A does not interrupt if a master parity error occurs. This bit is cleared at power-up.

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LSI 53C810A technical manual Zmod, Zsd, Srtm