NEC NDA-30115-001 manual Transmission Sequence

Property Management System - Communication Interface Architecture

Transmission Sequence

A Violation Code message will be sent to the PMS in the following cases:

•When the message counter does not match the number of characters received.

•When a station number not existing in the NEAX is specified in the message data from the PMS.

•Upon receipt of an invalid Wake Up time (e.g. 25:00).

The sequence of transmitting a message is slightly different for the PMS and NEAX. However, both sequences follow the same outline.

The party which desires to send must first bid for sender rights. This is done by sending the start sequence (see Figure 2-1). Once the start sequence has been sent and acknowledged, that party is now the “sender” and the other party is the “receiver”. (Unless both parties have simultaneously sent a start sequence. If this occurs, the PMS must relinquish sending rights to the NEAX.) The receiver must then respond with an answer control code (ACK, NAK, DLE <, DLE :, DLE ?) before the Sender Timer (see “Sender Timer” on page 10) expires.

If no answer control code is received, the sender will resend the start sequence and again wait for an answer control code.

When an answer control code is received, the sender must respond before the Receiver Timer (see “Receiver Timer” on page 10) expires. If the answer control code is an ACK, the sender must send the message. Again, the receiver must respond with an answer control code before the Sender Timer expires.

To finish the transmission sequence (regardless of its success), the sender must send an End Code (EOT) to release sending rights. Once that is done, both parties may begin the process over again by bidding for the sender rights.

In the transmission sequence figures that follow, these message names are used:

Table 2-4 Message Names

Name	Control Code	Explanation
Start Sequence	SA, UA, ENQ	Bid for sender rights
Message	STX, ..., ETX, BCC	Actual message sent
Query	ENQ	Query for expected answer control code
End Code	EOT	Release sender rights
Accept	ACK	Positive acknowledgment
Reject	NAK	Negative acknowledgment
No Answer	<Nothing>	Timer expired before an answer control
		code was received
Contention	Start Sequence	Simultaneous start sequences
Interrupt	DLE <	Request to release sender rights
Abort	DLE :	Demand to release sender rights
Pause	DLE ?	Receiver’s queue full; please wait

NDA-30115 Revision 1.0 Page 7