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Appendix D
Serial Port
Keystroke Emulation
Introduction
The serial port allows the PG-200 to be controlled from an external computer. The serial
port commands emulate PG-200 front-panel keystrokes wherever possible. As an
example, a “W” followed by a number (up to 3 digits), a unit (‘N’, ‘U’, or ‘M’) and a
“CR” constitute a command to change the pulse width. The pulse delay and trigger out
commands follow the same format. Since there are a limited number of front-panel
switches, many functions are achieved via the FUNCTION key. The same is also true for
RS-232 communications. To emulate a FUNCTION key operation, send an “F”,
followed by the function number.
Byte Rate
Although the serial parameters specify 9600 baud, this is only a bit rate. The byte rate is
much lower. The PG-200 can distinguish one ASCII character at 9600 baud, but if sent a
string of characters at this rate, the pulser will probably lock up. This is because the
serial input buffer is polled only about once every 100 ms. This slow rate occurs because
polling the serial port is a low priority task. The frequency of occurrence depends on
other pulser operations such as pulsing routines and setting the high voltage.
Echo
On receiving a complete character, the PG-200 echoes the character back to the control
source. Because the low baud rate, it is a good idea to have the control software detect
the echo before commencing transmission of the next character. This will assure reliable
communications with as high a data rate as possible. Software routines that perform the
required echo monitoring and data-flow control are available from PI for the PC DOS
platform. Contact the factory for additional information, if interested.
Command List
The RS-232 commands recognized by the PG-200 are as follows.
W
Set Width
D
Set Delay
O
Set Delayed Trigger
L
Trigger Level (enter a number between -10 and 10)
S
Trigger Select (toggles between Internal and External)
F
Function (enter number in range of 1 to 215). Chapter 5 describes the function
assigned to each number.
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