Page 6 NDA-30115 Revision 1.0
Architecture Property Management System - Communication Interface
The messages (but not the control codes or start sequence) sent between th e NEAX
and the PMS must have header and trailing sections as defined in the following
format:
Table 2-3 Base Message Format
The message format breaks down as follows:
•STX -- Start of text block. (One byte - 02H.)
•SA -- System Address. (One byte - ‘1’ [31H].)
•UA -- I/O Unit Address. (One byte - ‘!’ [21H].)
•EI -- Entry Index. (One byte - ‘L’ [4CH].)
•FTC -- Feature Code. (See below.) A list is provided in Appendix C, “Feature
Codes”.
•MSC -- Message Counter. This represents the length of the message. The cou nt
of characters starts at the FTC field and ends at t he last ch aracter of the body o f
the message, not including the ETX. If the ETX character does n ot immediately
follow the character specified by the message cou nter, an invalid message is
assumed.
•FC -- Function Code. This specifies the individua l operation a nd processing for
the feature designated by the Feature Code (FTC). A list is provided in
Appendix D, “Function Codes”.
•ETX -- End of text block. (One byte - 03H.)
•BCC -- Block Check Code. This is computed by an exclusive OR of the
message from the SA to the ETX (in clusive). 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.)
Feature Codes range in value from 00 to FF (hex). These codes define the “Major
Category Codes” for service features.
Codes from 80 to FF are used as “Violation Codes”. When a specific message
received from the PMS cannot be processed for some reason, 80 (he x) is added to
the received Feature Code so that it will be handled as a Violation Code. If the
NEAX regards a text as a Violation Code, the system data of the NEAX may be
assigned so that a text of this type is returned to the PMS. There fore, when the PMS
has received a Violation Code, provisions should be made for the PMS to print out
this violation.
Block Check Code Range02H ‘1’03H xx‘!’...01234 6 89
STX SA UA EI FTC MSC FC Message ETX BCC
Message Count Range‘L’