Seagate Ultra 320, Ultra 160 manual Pcrc signal usage requirements, Scsi target usage of Pcrca

During the SELECTION PHASE, RESELECTION PHASE, ST DATA PHASE, COMMAND PHASE, MESSAGE PHASE, and STATUS PHASE, this signal is referred to as DB(P_CRCA) and is sourced by the SCSI device port driving the Data Bus. The DB(P_CRCA) signal is associated with the DB(7-0) signals and is used to detect the presence of an odd number of bit errors within the byte. The DB(P_CRCA) bit is driven such that the num- ber of logical ones in the byte plus the parity bit is odd.

Data group transfers are enabled (see Section 4.3.12) when this signal is referred to as P_CRCA and is sourced by the target to control whether a data group field is a pad field, pCRC field, or data field (see Section 2.11.1). When asserted, the data group field shall be pad or pCRC fields that shall not be transferred to the application client. When negated, the data group field shall be a data field that shall be transferred to the appli- cation client.

During DT DATA phases when information unit transfers are enabled, this signal is referred to as P_CRCA and sourced by the SCSI target. Depending on the negotiated condition of read streaming and write flow control, the SCSI initiator and target usage for P_CRCA is different. When information unit transfers are enabled, the SCSI target and initiator shall use the P_CRCA signal as indicated in Table 2.

Table 2:	P_CRC signal usage requirements
Write flow		Read		SCSI initiator
				response to
control		streaming	DT Data phase	P_CRCA	SCSI target usage of P_CRCA
Disabled		Disabled	All	Ignore	Continuously negated.
Enabled		Disabled	DT DATA IN	Ignore	Continuously negated.
			DT DATA OUT	Monitor	Asserts to indicate when the current SPI data stream
					information unit is the last SPI data stream information
					unit of the current write stream.
Disabled		Enabled	DT DATA IN	Monitor	Asserts to indicate when the current SPI data stream
					information unit is the last SPI data stream information
					unit of the current read stream.
			DT DATA OUT	Ignore	Continuously negated.
Enabled		Enabled	DT DATA IN	Monitor	Asserts to indicate when the current SPI data stream
					information unit is the last SPI data stream information
					unit of the current read stream.
			DT DATA OUT	Monitor	Asserts to indicate when the current SPI data stream
					information unit is the last SPI data stream information
					unit of the current read stream.
A SCSI device is not required to use read streaming even if it is enabled
A SCSI device is not required to use write flow control even if it is enabled

P1 (Parity 1)—A signal normally sourced by the SCSI device driving the Data Bus. The P1 signal is associated with the DB(15–8) signals and is used to detect the presence of an odd number of bit errors within the byte The P1 bit is driven such that the number of logical ones in the byte plus the P1 bit is odd.

During the ST DATA PHASE with transfer length set for 8-bit transfers, COMMAND PHASE, MESSAGE PHASE, and STATUS phase, the P1 signal shall not be driven by any SCSI device.

During the SELECTION phase and the RESELECTION phase on a 16-bit wide bus segment the P1 signal shall be sourced by the SCSI device driving the DATA BUS.

When data group transfers are enabled (see Section 4.3.12), the P1 signal shall be continuously negated by the SCSI device driving the DB(15-0) signals and shall be ignored by the SCSI device receiving the DB(15-0) signals during DT DATA phases.

16 Parallel SCSI Interface Product Manual, Rev. A )