INFICON VGC403 Three-Channel Measurement and Control Unit - Manual (Page 32)

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tinb07e1-e 2011-07 Vacuum Gauge Controller
6 Computer interface
6.1 Basics
6.1.1 Connection
The Vacuum Gauge Controller is able to communicate
with a computer via a serial interface (RS232C). The con-
nection socket and the required connection cable are
described in Chapter 3.3.7 RS232C,  14.
6.1.2 Nomenclature
The following terms and symbolic styles will be used in
the description of the computer interface:
Tab. 6-1 Terms
Square brackets [...]
Square brackets identify optional parameters. The items
enclosed by the brackets may appear, but they are not
essential. The brackets are not actually used in the com-
mand.
Angle brackets <...>
Abbreviations enclosed by angle brackes identify control
characters. The entire expession including the brackets
is replaced by a numerical value. See Tab. 6-2,  32.
Tab. 6-2 Control characters
6.2 Communication
6.2.1 Protocol
The following protocol is used in the communication:
• 8 data bits
• No parity bit
• 1 stop bit
The baud rate can be selected. See Chapter 5.3.2 Baud
rate (bAud),  27. Hardware handshake is not used.
Messages are transferred as ASCII strings. Blanks
(spaces) in the string are ignored. The information is
exchanged bidirectionally, i.e. data and control com-
mands can be exchanged in both directions.
The input buffer of the Host must have a capacity of at
least 75 bytes.
6.2.2 Sending (Host --> Unit)
Messages of the Host are composed of mnemonics and
parameters. Mnemonics are command abbreviations and
always consist of three ASCII characters. See
Chapter 6.3 Mnemonics,  34. The control characters
<CR> or <CR><LF> signal the end of the message.
The Vacuum Gauge Controller checks every message it
receives. Afterwards it sends a positive or a negative
acknowledgement to the Host.
In a symbolic representation this process can be illus-
trated as follows:
Term Significance
Host Computer or terminal
Sending (S) Data transfer from the Host to the
Vacuum Gauge Controller
Receiving (R) Data transfer from the Vacuum
Gauge Controller to the Host
ASCII American Standard Code for Infor-
mation Interchange
Term Value Significance
<EXT> 03h End of text (Ctrl-C). Reset
the interface. Delete the
input buffer.
<ENQ> 05h Enquiry (Ctrl-E). Request
data transmission.
<ACK> 06h Acknowledge. Positive
acknowledge.
<LF> 0Ah Line feed. Line feed.
<CR> 0Dh Carriage return. Carriage
return.
<NAK> 15h Negative acknowledge.
Negative acknowledge.
Term Value Significance