4. Error Checking
This release is a “blind” protocol designed to be used when the data link is considered to be
100% reliable. Future release versions will contain error checking and retransmission.
5. Messages
With the exception of the message terminator, CR-LF, all characters are printable ASCII. C
source for generating a well-formed message string is provided in Appendix A. Contact Apex
Technical Support concerning the availability of an RS-232 demo program.
5.1. Packet Format
Data packets both from a PC to the panel and from the panel to a PC use the following
format. Note: All hex values are entered in upper case only.
NNMSD…
00
CC
(CR-LF)
Packet Length
NN
2 ASCII characters, length of packet including all characters but CR-LF at the end
of the packet. Legal values are hex 00 to FF. Permissible characters are ASCII 0-9 and upper
case A-F.
Message Type
M
1 ASCII character, message/packet type ID. These are upper and lower case alpha
characters. Upper case is used for responses from and panel and lower case for commands to
the panel. Allowed values are a-z and A-Z
Sub-Message Type
S
ASCII character, sub-message/packet type. These are upper and lower case alpha
characters. Upper case is used for responses from and panel and lower case for commands to
the panel. Allowed values are a-z and A-Z .
Data
D
… 0 or more ASCII characters of data associated with the command/packet type. Any
printable ASCII character is permitted.
Reserved
00 Two ASCII characters, reserved for future development. The only currently legal
character is 0 (numeric zero).
Checksum
CC
2 ASCII characters, 2-digit checksum. This is the hexadecimal two’s complement
of the modulo-256 sum of the ASCII values of all characters in the message excluding the
checksum itself and the CR-LF terminator at the end of the message. Permissible characters
are ASCII 0-9 and upper case A-F.
5
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