Stanford Research Systems SR844, User Manual

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Remote Operation 4-7
SR844 RF Lock-In Amplifier
Introduction
The SR844 RF Lock-In Amplifier may be remotely programmed via either the RS232 or
GPIB (IEEE-488) interfaces. Any computer supporting one of these interfaces may be
used to program the SR844. Both interfaces are receiving at all times, however, the SR844
will send responses to only one interface. Specify the output interface with the OUTX
command at the start of every program.
Important!
Use the OUTX command at the beginning of every program to direct the
SR844 responses to the correct interface.
Communicating With GPIB
The SR844 supports the IEEE-488.1 (1978) interface standard. It also supports the
required common commands of the IEEE-488.2 (1987) standard. Before attempting to
communicate with the SR844 over the GPIB interface, the SR844's Device Address must
be set with the
Setup
key.
Communicating With RS232
The SR844 is configured as a DCE ( transmit on pin 3, receive on pin 2) device and
supports CTS/DTR hardware handshaking. The CTS signal (pin 5) is an output indicating
that the SR844 is ready, while the DTR signal (pin 20) is an input that is used to control
the SR844's data transmission. If desired, the handshake pins may be ignored and a simple
3 wire interface (pins 2, 3 and 7) may be used. The RS232 interface Baud Rate and Parity
are set with the
Setup key. The RS232 word length is always 8 bits.
Indicators
To assist in programming, the SR844 has four interface status indicators located in the
INTERFACE section of the front panel.
The ACTIVE indicator flashes whenever a character is received or transmitted over either
interface.
The
ERROR
indicator flashes when an error, such as illegal command, or parameter out
of range, has been detected.
The
REMOTE
indicator is on whenever the SR844 is in the Remote state (front panel
may be locked out).
The SRQ indicator is on when the SR844 generates a service request. SRQ stays on
until a GPIB serial poll is completed.
Queues
To help find program errors, the SR844 can display its receive buffer on the displays. Use
the
Setup key to access the Queue display. The last 256 characters received by the
SR844 may be displayed in hexadecimal format. See the Chapter 3, Interface, for a
complete description.