Specifications

Remote Programming – Command List
47
Bit 4
Rate Error. This bit is set whenever a gate is
missed. This can occur if a gate delay or width
exceeds the trigger period minus 1 µs.
Bit 5
Recall Error. This bit is set if a recall from a stored
setting detects an error in the recalled data. If an
error is found, the instrument setup is not altered.
Bit 6
SRQ. This bit is always zero when polled via the
SS command. This bit is set in the status byte
which is read via the GPIB serial poll following a
service request generated by the SR400.
Bit 7
Command Error. This bit is set when an illegal
command is received.
SECONDARY STATUS BYTE
The secondary status byte is actually only a 3 bit
register. The secondary status byte is read using
the SI command and returns a value from 0 to 7 in
ASCII. The secondary status byte operates the
same as the status byte above except that it cannot
generate service requests.
The definitions for each bit of the status byte are
given below:
Bit 0
Triggered. This bit is set when the gate generator
is triggered.
Bit 1
Inhibited. This bit is set when the discriminators
are inhibited.
Bit 2
Counting. This bit samples the state of the
counters. If counting is in progress when this bit is
polled, a 1 is returned, otherwise a 0 is returned.
ERRORS/DATA WINDOW
Whenever a parameter out of range or an
unrecognized command error occurs, bit 7 of the
status byte is set and the ERR LED flashes. In
addition, any commands remaining on the current
command line (up to the next <cr>) are lost. To
aid in determining the cause of the error, the last
254 characters received by the SR400 may be
viewed on the LCD display using the DATA line
of the COM menu. The knob may be used to scroll
through the command buffer. The display always
returns to the most recent data whenever the menu
line is brought up or a new character is received.
Any command that clears the communication
buffers also clears this display window. This
includes changing any COM parameters, resetting
the instrument, or a buffer overflow.
TROUBLE-SHOOTING INTERFACE
PROBLEMS
If you are having difficulty getting your computer
to communicate with the SR400 look to the
following sections on the RS-232 and GPIB
interfaces for some tips specific to your particular
interface.
An ASCII terminal is a valuable aid for debugging
interface problems. You can use it to:
1) become familiar with the SR400's command
structure
2) substitute a human for the SR400 by using a
null modem cable ( to make the DTE a DCE ) and
attaching the terminal to the port to which you
would normally have connected the SR400. This
allows you to test your program's responses to
inputs which you provide from the terminal.
COMMON HARDWARE PROBLEMS
INCLUDE:
1) The RS-232 or GPIB cables are not properly
attached.
2) The COM parameters are incorrect for the RS-
232 interface or the GPIB address is not set
correctly (Make sure the RS-232 echo is off when
using the RS-232 interface with a computer.)
3) Your computer requires an RS-232 control line
to be asserted, but your cable does not pass it
between the SR400 and the computer, or, your