NDA-30115 Revision 1.0 Page 7
Property Management System - Communication Interface Architecture
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).
Transmission
Sequence The sequence of transmitting a me ssage is slightly different for the PMS a nd
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 se quence 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 cod e .
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 tha t is done, both parties
may begin the process over again by bidding for the sender rights.
In the transmission sequence figur es 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 se nder rights
Abort DLE : Demand to release sender rights
Pause DLE ? Receiver’s queue full; please wait