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16 Remote Commands
16.1
General
16.1.1
Remote and Local Operation
At power-on the instrument will be in the local state, with normal keyboard operation possible. All
remote interfaces are active and listening for a remote command. When any command is received
from any interface the instrument will enter the remote state. In this state the keyboard is locked out,
the display switches to the home screen, with the REM indicator displayed. The instrument may be
returned to the local state by pressing
[
Cancel]
(Local)
; however the remote state will be
immediately re-entered if the instrument is addressed again or receives another command from any
interface. It is the responsibility of the user to avoid any conflict if parameters are changed from the
front panel while in the Local state.
16.1.2
Remote Command Handling
Each remote control interface has a separate input queue which is filled, under interrupt, in a
manner transparent to all other instrument operations. The RS232 interface implements flow control
by sending XOFF when the queue contains approximately 200 characters, and then XON when
about 100 free spaces become available. All the other interfaces have standard automatic flow
control mechanisms built into their physical layer communication protocol.
Commands are taken from the input queues by the parser as available. Commands and queries
from each queue are executed in order, but the order of execution of commands from different
interfaces is not defined and should not be relied upon. The parser will not start a new command
until any previous command or query is complete. Responses are sent to the interface which issued
the query. There is no internal output queue, so on the GPIB interface the response formatter will
wait, indefinitely if necessary, until the complete response message has been read by the controller,
before the parser is allowed to start the next command in the input queue. On all other interfaces
the response message is immediately sent into buffers in the physical layer.
16.1.3
Remote Command Formats
Commands are sent as
<PROGRAM MESSAGES>
by the controller, each consisting of zero or more
<PROGRAM MESSAGE UNIT>
elements, separated (if there is more than one such element) by
<PROGRAM MESSAGE UNIT SEPARATOR>
elements, and finally a
<PROGRAM MESSAGE TERMINATOR>
.
The
<PROGRAM MESSAGE UNIT SEPARATOR>
is the semi-colon character ';' (3B
H
).
The
<PROGRAM MESSAGE TERMINATOR>
, which separates or terminates
<PROGRAM MESSAGES>
, is the
new line character (0A
H
), but in the case of the GPIB interface the hardware
END
message may also
be used, either with the last character of the message or with the new line.
A
<PROGRAM MESSAGE UNIT>
is any of the commands in the remote commands list, which must be
sent in full as specified. A command must be separated from any parameters by
<WHITE SPACE>
(which is defined as the character codes 00
H
to 20
H
inclusive, excluding the new line character
0A
H
). No
<WHITE SPACE>
is permitted within any command identifier or parameter, but any other
additional
<WHITE SPACE>
is ignored. Note that the Backspace character (07
H
) is treated as
<WHITE
SPACE>
, so it cannot be used to delete incorrect characters, and will not hide the error.
The high bit of all characters is ignored and all commands are case insensitive. Commands that
require a numeric parameter accept the free form
<NRF>
format; text parameters must be sent as
Character Program Data <
CPD
> as specified.
<NRF>
numbers must be in basic units, may have a decimal point and fractional part, and can
include an exponent part if helpful. They are rounded to the precision supported, so 12, 12.00,
1.2e1, 120e-1 are all accepted as the number 12.
