Lake Shore 234, Руководство пользователя

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Lake Shore Model 234/234D User’s Manual
Remote Operation 4-3
When programming a Model 234 from the serial interface, consider the
following:
• The serial interface transmission mode (asynchronous half duplex), format
(10 bits per character; 1 start, 8 data, no parity, and 1 stop), and baud rate
(9600) are factory set as outlined in Paragraph 4.1.
• End of string terminators are fixed at (CR)(LF).
• At 9600 baud, each character takes about 1 millisecond to transmit. Some
host computers DMA serial interface access. Programs must allow for
transmission time delay before looking for a query response.
• The unit stores received characters in a 16-character buffer. After
receiving terminators, the unit responds to a query, if requested, and
stores any new parameters. The unit requires about 50 milliseconds to
store new parameters before it can receive any new commands (it
requires 3 seconds for curve parameters, and 10 seconds for input
calibration). The second command string of multiple command strings sent
less than 50 milliseconds (or 3 seconds or 10 seconds) apart is ignored or
returns a unpredictable response.
• The unit implements new parameters and updates measurement data
internally once per 250 millisecond operation cycle (500 milliseconds for
Scale 0). Sending new parameters or data requests at a rate faster than
2 Hz (or 1 Hz) is not recommended.
4.1.3 QuickBasic Programming Considerations
When communicating with a unit using a QuickBasic program, do not use
the LINE INPUT # statement to retrieve data from the unit. The LINE INPUT
# statement reads all characters from a data file up to a carriage return (CR)
and then skips over the carriage return line feed (CR)(LF) sequence. The
LINE INPUT # statement does not work this way for the communications
port. It reads characters up to the (CR) and continues program operation
while the unit transmits the (LF). In most cases, the (LF) remains as the first
character of the next input. This could cause communications contention
problems.
The QuickBasic 4.5 manual, Section 3.5.2 Communications through the
Serial Port, reads, “Since every character is potentially significant data, both
INPUT # and LINE INPUT # have serious drawbacks for getting input from
another device. This is because INPUT # stops reading data into a variable
when it encounters a comma or new line (and, sometimes, a space or
double quote), and
LINE INPUT # stops reading data when it encounters a
new line. This makes INPUT$ the best function to use for input from a
communications device, since it reads all characters.”
The program in Paragraph 4.1.4 uses the INPUT$ function instead of the
LINE INPUT # statement to retrieve responses from the Controller.