Stanford Research Systems SR620, Руководство пользователя

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Programming Commands 29
SR620 Universal Time Interval Counter
PROGRAMMING THE SR620
The SR620 Universal Time Interval Counter 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 SR620. Both interfaces are active at
all times: the SR620 will send responses to the
interface which asked the question. All front and
rear panel features (except power) may be
controlled.
Communicating with GPIB
The SR620 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 SR620 over the GPIB interface, the SR620's
device address must be set. The address is set in
the CTRL submenu of the CONFIGuration menu
and may be set between 0 and 30.
Communicating with RS232
The SR620 is configured as a DCE (transmit on
pin 3, receive on pin 2) and supports CTS/DTR
hardware handshaking. The CTS signal (pin 5) is
an output indicating that the SR620 is ready, while
the DTR signal (pin 20) is an input that is used to
control the SR620's transmitting. 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, number of data bits,
and parity must be set. These may be set in the
CTRL submenu of the CONFIGuration menu. The
RS232 delay programs the time interval between
the SR620's transmitted characters if no
handshaking is used. The delay is equal to 2ms
times the setting and is usually set to 0 (no delay).
However, some slower computers may require a
delay. The RS232 echo should be set OFF if the
SR620 is connected to a computer. It may be ON
if connected to a terminal or a terminal emulation
program.
RS232 echo and no echo operation
When the RS232 echo mode is ON the SR620 will
echo all characters sent to it , will send linefeeds in
addition to carriage returns, and will return the
prompts -> and ?> to indicate that a command
was either processed correctly or contained errors.
The RS232 echo mode is good way to become
familiar with the commands that the SR620
expects and the values that it will return . When
the unit is controlled by a computer, the echo
feature should be turned OFF.
Front Panel LEDs and data window
To assist in programming, the SR620 has 3 front
panel status LEDs. The ACT LED flashes
whenever a character is received or sent over
either interface. The ERR LED flashes when an
error has been detected, such as an illegal
command, or parameter out of range. The REM
LED is lit whenever the SR620 is in a remote state
(front panel locked out).
To help find program errors, the SR620 has an
input data window which displays the data
received over either the GPIB or RS232
interfaces. This window is the first menu line in the
CTRL submenu and displays the received data in
hexadecimal format.One may scroll back and forth
through the last 256 characters received using the
SCALE up/down arrow keys. A decimal point
indicates the most recently received character.
Command Syntax
Communications with the SR620 use ASCII
characters. Commands may be in either UPPER
or lower case and may contain any number of
embedded space characters. A command to the
SR620 consists of a four character command
mnemonic, arguments if necessary, and a
command terminator. The terminator may be
either a carriage return <cr> or linefeed <lf> on
RS232, or a linefeed <lf> or EOI on GPIB. No
command processing occurs until a command
terminator is received. All commands function
identically on GPIB and RS232. Command
mnemonics beginning with an asterisk "*" are
IEEE-488.2 (1987) defined common commands.
These commands also function identically on
RS232. Commands may require one or more
parameters. Multiple parameters are separated by
commas ",".
Multiple commands may be sent on one command
line by separating them by semicolons ";". The
difference between sending several commands on
the same line and sending several independent
commands is that when a command line is parsed
and executed the entire line is executed before
any other device action proceeds. This allow