Operation and Maintenance Manual

4.3 Serial Protocol - Commands from Host Computer to
ACU
All commands use printable ASCII characters, plus the ASCII control codes
as follows:
STX (start of text, value 02 hex)
ETX (end of text, value 03 hex)
Each command line sent to the controller consists of an ASCII STX character,
followed by up to 80 characters of commands, two checksum characters, and
an ETX character. The checksum is calculated such that the sum modulo 256
of all command line bytes (excluding the STX, ETX, and checksum bytes)
will be equal to the checksum characters interpreted as ASCII-HEX.
The command line consists of a number of commands, each of which is either
a read command or a write command.
A write command consists of a 3-letter command followed by a value. The
value consists of a number with an optional leading sign (+ or -), up to 8
digits, and an optional decimal point. For each parameter, there is a range of
legal values. Certain commands will be received only when the controller is
in the remote mode.
A read command consists of a 3-letter command followed by the read-request
symbol "<". Only one read request is allowed in a single command line. Any
parameter may be read at any time.
Several characters, such as space, tab, new-line, carriage return, comma, and
semicolon, are ignored. They may be included in the command line at any
place and will have no effect, other than to add to the time required to send the
command line. They are not counted in the 80 character limit. However, they
must be included in the checksum. These characters may be used, if desired,
to provide the meaning of a command line by adding descriptive comments.
If any error is detected in a command line, none of the commands in the line
are executed.
A full list of the commands, parameters, maximum and minimum values, and
conditions governing when they may be written, is provided in section 4.5.