Omega Engineering CN8240, CN8260 manual Omega+ Protocol, Message Formats, Start Char, Zone, Example

CN8240 & CN8260 Series Communications & Options

Digital

Communications Option

Omega+ Protocol

The Omega+ Protocol provides an easy way to query and modify controller parameters using a personal computer and the optional digital communications option of the 18C/25C.

In this manual, the word “host” refers to the personal computer that’s communicating with the controllers in the serial link, and the word “slave” refers to the controllers themselves.

All transactions between the host and the slaves are done with messages consisting of only printable ASCII charac- ters. There are only two primary types of messages: Requests and Responses. Messages coming from the host are called requests and messages coming from the slaves are called responses.

With the exception of a broadcast request, for every request sent from the host, the slave will send back a response. If a slave does not respond within 100 milliseconds, then the request can be considered lost.

A broadcast request is a request having an ID of ‘00’ (see Message Formats below). It is used to address all slaves on the network. All slaves on the network will perform the actions requested in a broadcast message. However, a response message will not be returned. Therefore, the host can only broadcast Write or Auxiliary Command Requests. All slaves will ignore all Read Broadcast Requests.

Message Formats

All Omega+ messages adhere to the general format of:

[START CHAR][ID][ZONE][TYPE][PARAM][ERROR][DATA][CHKSUM][END CHAR]

START CHAR

This is a single character which designates the start of the message. For a Request message, this character is the ASCII ‘$’ and for a Response message, this character is the ASCII ‘%’.

ID

This is a two-character ID identifying the receiving controller. Controller IDs go from 1-255 inclusively and all slaves in the network must have unique IDs. The ID number of ‘00’, when used in a request, designates a broadcast mes- sage that is used to address all controllers in the network. See the section Request Message for an explanation of the broadcast message.

In order to represent 255 with just two ASCII characters, a number system known as the Message Code Numbering System is used. In this system, the most significant digit is represented with the numbers 0-9 and the letters A-Z and the least significant digit is represented with the numbers 0-9.

The numbers 0-9 have the same values as their decimal counterparts and the letters A-Z have the values of 100 - 50 inclusively in increments of 10.

	Example:
Message Code Value	=	Decimal Value
00		0 + 0 = 00
99		90	+ 9 = 99
A0		100	+ 0 = 100
A2		100	+ 2 = 102
B8		110	+ 8 = 118
P5		250	+ 5 = 255

Zone

This is a two character ID identifying the Zone number in multi-zone capable controllers. For the 18C/25C, this num- ber must be 01.

6