SRS Labs SR640 Series, Manual

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9
The SR640 dual channel low-pass filter is remote-
ly programmable via both RS-232 and GPIB inter-
faces. All front panel features (except offset adjust-
ment) may be controlled and read via the
computer interfaces.
Communicating with the SR 640
Before using either the RS-232 or GPIB interface,
the appropriate configuration switches must be
set.
The configuration switch is located on the
rear panel and label 'SW1'. Bit 8 of the switch se-
lects GPIB or RS-232 operation. If bit 8 is 'on',
GPIB operation is selected, if it is 'off', the RS-232
interface is enabled.
The other bits of the switch
take their meaning depending upon whether RS-
232 or GPIB operation has been selected.
When a bit is 'on', it is in the DOWN position.
GPIB:
Bit Explanation
8
Always on for GPIB
7 not used
6 not used
5 high order bit of GPIB address
4 GPIB address (on = 1 off = 0)
3 GPIB address
2 GPIB address
1 low order bit of GPIB address
R S-232:
Bit Explanation
8
Always off for RS-232
7 on = echo off = no echo (normally
off)
6 on = 8 bit word off =7 bit word
5 on = even parity off = odd parity
4 on = parity enabled off = disabled
3 baud rate select
2 baud rate select
1 baud rate select
Bit 3 2 1 Baud Rate
on on on 19200
on on off 9600
on off on 7200
on off off 4800
off on on 3600
off on off 2400
off off on 2000
off off off 1800
Note that the configuration switch is only read on
power-up. If a setting needs to be changed, the
unit must be turned off and turned on again for the
change to be recognized.
G UIDE TO PROGR AMMING
Command Syntax
Communication with the SR640 is accomplished
by sending and receiving strings of ASCII charac-
ters.
Characters sent to the SR640 may be sent
in either UPPER or lower case.
A command to the SR640 consists of 4 ASCII
characters followed by an optional question mark
'?' character, followed by a list of arguments separ-
ated by commas, followed by a line-feed (<lf>)
character.
If spaces are included in the com-
mand string, they are ignored by the SR640. The
SR640 interprets the GPIB EOI message sent with
the last character of a string as equivalent to a <lf>
terminator.
Examples of commands are:
FREQ1,23600.<lf> set the channel 1 filter
frequency to 23.6 kHz.
FREQ?2<lf> read the channel 2 filter
frequency
*CLS<lf> clear the status byte
Multiple commands may be sent on a single line.
The commands must be separated by semicolon
characters. An example of a multiple command
would be:
FREQ1,23.6E3;FREQ2,100<lf>
The presence of a question mark character in a
command indicates that the command is a request
to the SR640 to send back a value. Values re-
turned by the SR640 are terminated with a car-
riage return <cr> and a linefeed <lf>.
If the GPIB
interface is used, the <lf> is accompanied by the
EOI message.
R S-232 Echo and No Echo Operation
In order to allow the SR640 to be operated from a
terminal, an echo feature has been included which
causes the unit to echo back characters received
over the RS-232 port.
This feature is enabled by
setting bit 7 of the configuration switch on. When
using the unit with a computer, this feature should
be disabled to prevent spurious characters from
being sent to the computer.
The echo feature is
not operational when the unit is being used with
the GPIB interface.
TIps on Using National Instruments
GPIB cards
To successfully interface the SR640 to a PC via
the GPIB, the instrument, interface card, and inter-
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