C156-E097-01EN 7 - 377.6 Bus ConditionsTwo types of asynchronous operations, an ATTENTION condition and a RESET condition, areprovided to control and modify the bus phase transition sequence (bus condition).7.6.1 ATTENTION conditionThe ATTENTION condition allows an INIT to report that the INIT has messages to be sent tothe TARG. The TARG receives a message from the INIT by executing the MESSAGE OUTphase. Figure 7.16 shows the ATTENTION condition.(1) Generation and release of ATTENTION condition (INIT)By making the ATN signal true, the INIT can generate the ATTENTION condition any timeexcept during the ARBITRATION or BUS FREE phase.Consider the generation of a new ATTENTION condition in the INFORMATION TRANSFERphase. To inform the TARG of the ATTENTION condition before the transition to the next newbus phase, the INIT must set the ATN signal true before 90 ns (Deskew Delay × 2) or more fromthe timing of setting the ACK signal false for the last byte being transferred in the current busphase. If the ATN sending timing is delayed, the TARG may not be informed of theATTENTION condition until the next bus phase. The INIT may not operate as it should.When transferring message information in several bytes in the MESSAGE OUT phase, the INITmust keep the ATN signal true. The INIT can make the ATN signal false any time except whilethe ACK signal is true in the MESSAGE OUT phase. When transferring the last byte in theMESSAGE OUT phase, the INIT generally makes the ATN signal false during the periodbetween the time the REQ signal becomes true and the time it returns the ACK signal. In thiscase, the INIT must set the ATN signal false before 90 ns (Deskew Delay × 2) or more from thetime of setting the ACK signal true.The INIT must make the ATN signal false before making the ACK signal true to transfer the lastmessage byte if so specified for the particular type of message to the TARG. (See Subsection2.1.2.)
