In order to indicate its intentions of sending this message, the initiator shall assert the ATN signal prior to its release of the ACK signal for the REQ/ACK handshake of the message byte that has the parity error. This provides an interlock so that the target can determine which message byte has the parity error. If the target receives this message under any other circumstance, it shall signal a catastrophic error condition by releasing the BSY signal without any further information transfer attempt (see 6.1.1).
If after receiving the MESSAGE PARITY ERROR message the target returns to the MESSAGE IN phase before switching to some other phase, the target shall resend the entire message that had the parity error.