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NDA-30115 Revision 1.0 Page 31
Property Management System - Communication Interface Message Formats
Chapter 4 Message Formats
All messages sent between the NEAX and the PMS must have header and trailing
sections as defined in the following format:
Figure 4-1 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. Used in conjunction with the Function Code to uniquely
identify a message. A list of values are included in Appendix C, “Feature
Codes”. (Two bytes.)
• MSC -- Message Count. This is the number of bytes from the FTC character up
to the character before the ETX. (Two bytes.)
• FC -- Function Code. This entry is dependent on the FTC entry. A list of values
are included in Appendix D, “Function Codes”. (One byte.)
• 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 (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.)
Note 1:
Unless otherwise noted, if the data to be stored in a message field has fewer char-
acters than the size of the field, all data must be left justified and the remaining
characters must be filled with space (20H) characters.
Note 2:
In the message diagrams, the STX, SA, UA, EI, FTC, MSC, FC and ETX fields
will show the actual entries needed. The remaining fields will have the name of
the field in the box and the length of the field below. For all fields, the beginning
byte number is listed on the top of the field.
Block Check Code Range
02H ‘1’ 03H xx‘!’
** Options defined below
...
01234 6 89
STX SA UA EI FTC MSC FC Message ETX BCC
** ** **
Message Count Range
‘L’