Stanford Research Systems SR620, Руководство пользователя

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Troubleshooting Tips 59
SR620 Universal Time Interval Counter
Be certain that your GPIB controller has been
configured to accept this sequence.
RS-232 PROBLEMS
The RS-232 baud rate, number of bits per
character, and parity bit definition must be set in
the "ctrL" section of the CONFIG menu. The
SR620 always sends two stop bits, and will
correctly receive data sent with either one or two
stop bits.
When connecting to a PC, use a standard PC
serial cable, not a "null-modem" cable. The SR620
is a DCE (Data Communications Equipment)
device, and so should be connected with a
"straight" cable to a DTE device (Data Terminal
Equipment). The "minimum" cable will pass pins
2,3 and 7. For hardware handshaking, pins 5 and
20 (CTS and DTR) should be passed.
Occasionally, pins 6 and 8 (DSR and CD) will be
needed: these lines are always asserted by the
SR620.
There are several software problems which may
occur when using the RS-232 interface:
1) You have sent the wrong command to ask for
data from the SR620. Your program may wait
forever for a response which will not come.
This may not be your fault: we have seen
Microsoft's Interpreted Basic on an IBM PC
occasionally send a curly bracket (ASCII 253)
when it was suppose to have sent a carriage
return (ASCII 13).
2) Your computer's baud rate was changed by a
previous program and no longer matches the
baud rate set for the SR620. Good
programming practice requires that you set the
computer's baud rate at the start of each
application program.
3) The initial command sent to the SR620 was
invalid due to a garbage character left in the
SR620's command queue from power-up, or,
the first character in your computers RS-232
UART is garbage from when the SR620 was
turned "ON". It is good practice to send a few
carriage returns to the SR620 to flush its
command queue. Also, your program should
read and ignore any characters which may be
left in the computer's UART.
4) The SR620 is not sending the correct 'end-of-
record' marker for your computer. For
example, it appears that some FORTRANs
require two carriage returns for an end-of-
record marker. The "ENDT" command may be
used to set the end-of-record sequence. (The
end-of-record marker is that sequence which
indicates a response is complete. From a
keyboard, a single carriage return is the end-
of-record marker.)
5) Answers are coming back from the SR620 to
fast, overwriting previous responses before
the computer can get them. To increase the
dwell time between characters, use the "WAIT
n" command. The dwell time between
characters will be 2n ms.
6)
The RS-232 echo must be "OFF", otherwise
all characters sent to the SR620 will be
echoed back to the source. (See the section
on "Configuration Menus" for details on RS232
configuration.) The computer will most likely
confuse echoed commands with the desired
data.