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NDA-30115 Revision 1.0 Page 13
Property Management System - Communication Interface Architecture
Transmission
Protocol
The messages sent between the NEAX and the PMS must have header and trailing
sections as defined in the following format:
Figure 2-5 Base Message Format
The elements of the message is as follows:
• PAD-L -- The leading pad character. (One byte - 55H.)
• SYN -- Synchronization character. At least three of these should be transmitted.
(One byte each - 32H.)
• STX -- Start of text block. (One byte - 02H.)
• Data -- The message data is describe below in Figure 2-6.
• ETX -- End of text block. (One byte - 03H.)
• CRC-- Cyclic Redundancy Check. This is computed by an exclusive OR of the
message from the SA to the ETX (inclusive). Detection of an STX starts the
computation (but the STX is not included). Detection of an ETX stops the
computation (and the ETX is included). (One byte.)
• PAD-T -- The trailing pad character. (One byte - FFH.)
The message data is defined as follow:
Figure 2-6 Message Data Format
Cyclic Redundancy Check Area
02H 03H xx
STX Data ETX CRC PAD-T
FFH32H55H 32H 32H
PAD-LSYN SYN SYN
02H ‘1’ 03H‘!’ ...
STX SA UA EI FTC MSC FC Message ETX
Message Count Range
‘L’