1.6.5.2 Synchronous Mode - Fujitsu MAN3184 SERIES Specifications

c. Improved Error Detection for the Asynchronous Information Phases (AIP)
The COMMAND, MESSAGE and STATUS asynchronous information transfer phases except
DATA phase only transfer information on the lower eight data bits of a SCSI bus with only
normal parity protection on those transfers. In this improved detection additional check
information can be transferred on the upper eight data bits. This error detection can improve
error detection capabilities. Since the upper eight data bits of the SCSI bus are used for this
scheme, this error detection method is only available on wide SCSI devices that are on wide
SCSI buses.
The additional check information is called "protection code". This code contains 21-bit code
word and covered signals of the 16-bit SCSI data bus. Protection code checking is enabled or
disabled on an I_T nexus basis. Protection code checking is disabled in the following case:
- After a power cycle
- After a hard reset
- After a TARGET RESET message
- After a change in the transceiver mode (i.e, LVD mode to MSE mode)
A SCSI device enable protection code checking for an I_T nexus when it detects that valid
protection code data is being transmitted on the upper byte of the SCSI bus. The following are
some possible times when a SCSI device could try to enable protection code checking:
- During the first COMMAND, MESSAGE or STATUS phase
- After a UNIT ATTENTION condition
- During the MESSAGE phase of a negotiation
Protection code errors are handled exactly parity errors during COMMAND, MESSAGE or
STATUS phases. But this parity error outputs will be logically OR'd into the existing parity
error logic. There are the some kinds of "parity error" as follows:
- DT mode CRC error
- DBP1, DB15-8 negated
- DBP1, P_CRCA parity error
- Protection code error
The kind of parity error isn't determined and when the device detected parity error, the device
proceeds to the next procedure without retry. The detail of the procedure is discribed in
CHAPTER 3, ERROR RECOVERY.

1.6.5.2 Synchronous mode

Synchronous data transfer is optional and is only used in DATA phases. It shall be used in a
DATA phase if a synchronous data transfer agreement has been established. The agreement
specifies the REQ/ACK offset and the minimum transfer period.
When synchronous data transfers are being used data may be transferred using ST data transfers or,
optionally, DT data transfers. DT data transfers shall only be used on 16 bit wide buses that
transmit and receive data using LVD transceivers.
The synchronous transfer mode allows information transfer with REQ and ACK signal check by
their pulse count (called the offset interlock). This mode can be used in the DATA phase only.
C141-E123-01EN 1 - 55