D U N I W A Y S T O C K R O O M C O R P .
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Analog Output - volts
pressure
0.10
1.6 x 10
-10
Torr (or mbar)
0.50
1.0 x 10
-9
1.00
1.0 x 10
-8
1.10
1.6 x 10
-8
2.00
1.0 x 10
-6
3.50
1.0 x 10
-3
4.00
1.0 x 10
-2
NOTE
The analog output is valid for the gauge which is selected on the display.
D. Serial Interface
The RS-232 serial port gives pressure readings when requested by the terminal. The interface is
standard RS-232 format; 9600 baud, 8-bits, no parity, 1 stop bit. The interface is through the 15-
pin D-sub accessory connector, see fig. 2, page 4 and fig. 3, page 5.
pin 7 is Tx (signal from the 921 to the terminal)
pin 8 is Rx (signal from the terminal to the 921)
pin 9 is return (ground).
The serial port allows reading pressure and other parameters of the 921; it is not possible to mod-
ify stored parameters over the serial port.
The following commands are used in the 921:
1.
Pressure
To read the pressure:
Send “p” (ASCII value 112); the 921 sends pressure to the terminal. Output is in the format:
A.Be-C
where A.B is the multiplier and -C is the exponent
Some examples follow:
displayed pressure
Serial Output
OFF
Off
OP
Open (lower than 1.0 x 10
-10
)
1.0 x 10
-9
Torr
1.0e-9
3.4 x 10
-8
Torr
3.4e-8
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