Handbook
November 2011
/
59-UMC0071
/
Issue
01
Mercury
iTC
Page 97
REMOTE OPERATION
Original Instructions
&
(Ampersand)
instructs an instrument to ignore any following ISOBUS control characters. This
character is not used by the iTC. The command allows instruments that include
@
,
$
,
&
or
!
characters in their command set to be used on ISOBUS.
!n
(Exclamation)
instructs the instrument that, from now on, its ISOBUS address is
n
. This command
must not be used if more than one instrument is connected to ISOBUS, as it will set
all connected instruments to the same address. This command does not affect the
instrument
`
s GPIB address.
NOTE: Use the $ command with caution, as it suppresses all responses, including the
? error response. Thus the computer cannot determine if a command has been
received.
NOTE: If a command is to be addressed to a specific instrument, but no reply is
required, it is permissible to use $ and @n together. The $ must always come
first.
NOTE: The ! command is only obeyed if a U command followed by a non-zero
password is sent first. This is to avoid accidentally changing an instrument
address.
7.4
GPIB interface
The GPIB interface supplements, rather than replaces, the RS232 serial interface. An
instrument can be controlled either by GPIB or by RS232, but not by both
simultaneously.
7.4.1
Switching between RS232 and GPIB operation
If the iTC is using RS232 and GPIB has not been deliberately disabled, the instrument
can be switched to GPIB operation at any time by asserting the GPIB IN-USE state. This
occurs automatically when a GPIB controller asserts the REN line and addresses the
interface to either talk or listen at the selected GPIB address.
Once the instrument is in the GPIB IN-USE state, it remains in that state until electrical
power is removed or the instrument is reset.
7.4.2
Sending commands via the GPIB
Commands sent via the GPIB follow the same syntax as commands on the RS232
interface. Commands must be terminated by a
Carriage Return
. A
Line Feed
may be
sent, if desired, but the iTC ignores it.
The iTC always accepts GPIB commands unless it is in TEST mode.
If a command produces a response message, the controller must read the response
before sending a further command.