General Information
Chapter Nine: RS-232 Communications
256
MKS RS-232 Protocol
Command formats sent by the Host computer
Messages sent by the host computer to the 146 unit are either commands that instruct the
instrument to change an operating parameter, or requests that prompt the instrument to report
status information. The following table shows the format of RS-232 command messages that are
sent from the host computer to the 146 unit. Specific commands are described in Command
Messages, page 259.
Note
Use UPPERCASE letters for all messages. Messages entered in
lowercase will generate an “invalid command” error.
Channel Numbering
The 146 unit can hold up to five plug-in boards and supports up to four input channels and one
process control channel. The input channels include capacitance manometers, Pirani gauges,
convection gauges, hot cathode gauges (maximum of two), cold cathode gauges, thermocouple
gauges, and mass flow controllers. The unit supports one process control channel. The analog
output(s) does not require channel space. The channel numbering sequence depends on the
position of the plug-in board in the 146 unit. The input and output channels are numbered
separately.
The 146 unit assigns the channel numbers upon power up. For example, using the board
configuration shown in Figure 4, page 27, the Pirani board in slot 1 would be assigned input
channel 1 (upper connector) and input channel 2 (lower connector). The Capacitance Manometer
board in the adjacent slot would use input channel 3. The Cold Cathode board in slot 3 would be
assigned input channel 4. The Auxiliary Output board in slot 4 provides two additional relays
and two additional analog outputs. Neither relays nor analog outputs are allocated channel
numbers. The Control board in slot 5 would use the one process control channel.
If the Capacitance Manometer board is removed from slot 2, the Cold Cathode board (previously
input channel 4) would become input channel 3, and all user defined parameters for the cold
cathode would change to default values. The parameters associated with input channels 1 and 2
remain unchanged because the channel numbers assigned to the Pirani board would have
remained unchanged.
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