NEC NDA-30115-001 manual Message Formats, 02H ‘1’ ‘!’ ‘L’ 03H

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:

0 1 2 3 4 6 8 9

02H

‘1’

‘!’

‘L’

**

**

**

...

03H xx

STX SA UA EI FTC MSC FC Message ETX BCC

Message Count Range

Block Check Code Range ** Options defined below

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.

NDA-30115 Revision 1.0 Page 31