Omega A2400 - Manual (Page 22)

Chapter 4
A2400 Command Set
The A2400 operates with a simple command/response protocol to control
all module functions. A command must be transmitted to the A2400 by the
host computer or terminal before the A2400 will respond with useful data. A
module can never initiate a communications sequence. A list of available
commands and a sample format for each command is listed in Table 4.1.
The following text describes the protocol normally used with the A2400. In
addition to the normal operation there are two other modes of operation
called the Extended Address mode and the Transparent mode. For larger
systems, the Extended Address protocol described in Chapter 7 may be
more appropriate. The Transparent mode is for systems that use non-D
series protocols. Transparent mode is described in Chapter 8.
Command Structure
Each command message from the host must begin with a command prompt
character to signal to the modules that a command message is to follow. For
standard addressing there are two valid prompt characters; a dollar sign
character ($) is used to generate a short response message from the
module. A short response is the minimum amount of data necessary to
complete the command. The second prompt character is the pound sign
character (#) which generates long form responses (the long response
format will be covered later).
The prompt characters must be followed by a single ASCII character
address identifying the module to which the command is directed. Each
module attached to a common communications port must be setup with its
own unique address so that commands may be directed to the proper unit.
Module addresses are assigned by the user with the SetUp (SU) command.
For ease in debugging, printable ASCII characters such as ‘1’ (ASCII $31)
or ‘A’ (ASCII $41) are the best choices for address characters.
The address character is followed by a two or three character command
which identifies the function to be performed by the module. All of the
available commands are listed in Table 4.1 along with a short function
definition. All commands are discussed in full detail later in this chapter. All
commands must be transmitted as upper-case characters.
A two character checksum may be appended to any command message as
a user option. See ‘Checksum’ section below.