Oxford Instruments Mercury iTC, Handbook

Page: 96 / 146

Handbook
November 2011 / 59-UMC0071 / Issue 01
Mercury iTC
Page 96
REMOTE OPERATION
Original Instructions
7.2.1 Commands and responses
Commands sent to the iTC consist of a single letter, optionally followed by a numeric
parameter, terminated by a
Carriage Return . All common operation commands are
based on upper-case letters. Lower case letters are used for some of the more
specialised commands.
The response sent by the iTC varies depending on the command. Usually the response
consists of the command letter received, followed the value of any data requested. If a
command instructs the iTC to perform an action rather than to send data, the response
is just the command letter.
If a command is not recognised, has an illegal parameter, or cannot be obeyed for any
reason, and error response is sent. This consists of a
? (question mark), followed by all
or part of the command string that produced the error. To simplify error handling in the
computer, the
? is always the first character returned.
The most common reason for a command error is attempting to execute a command
while the iTC is in LOCAL mode. The
X command can be used to determine the present
status of the iTC to prevent this type of error.
7.2.2 Numeric parameters
All numeric parameters are treated as signed decimal numbers, and are sent as a string
of decimal digits with a decimal point in the appropriate place.
7.3 Control via ISOBUS
To allow separate instruments on the bus to be distinguished, each instrument is
allocated a unique address in the range 0 to 9.
When more than one instrument is connected to ISOBUS, all commands must start with
a special ISOBUS control character. If the control character is omitted, all instruments
connected to ISOBUS will reply together.
NOTE: Omitting the control character will result in lost data, but will not cause
hardware damage.
The command following the control character (and any required parameter) follows the
form described in
Section 7.2 .
The response of the instrument depends on the initial control character:
@n (At)
addresses the command to instrument number n , where n is a digit in the range 0 to
9. The instrument obeys the command and returns its usual response. All other
instruments ignore the command and send no reply.
$ (Dollar)
instructs all instruments to send no reply. This character is normally sent before a
command that is sent to all instruments simultaneously. This prevents the
instruments from echoing the command together, which would cause a conflict.