INFICON SKY CDGxxxD User Manual
Communication Protocol
RS232C
Serial Interface
CDG025D, CDG045D,
CDG100D, CDG160D,
CDG200D
RS232C
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General Information
The RS232C Serial Interface permits the communication between the digital
INFICON Capacitance Diaphragm Gauge and
• an INFICON Vacuum Gauge Controller (VGC series) or
• another appropriate controller.
The RS232C Serial Interface integrated in the Capacitance Diaphragm Gauge
allows to digitally transmit measurement values and information on the gauge
status as well as to make parameter settings.
Functional Principle
Data format
Transmission rate
Pin assignment
Caution
Caution: data transmission errors
Any attempt to simultaneously operate the gauge via the RS232C
Serial Interface and a fieldbus interface (DeviceNet or Profibus) or the
diagnostic port may result in incorrect data and data transmission
errors.
Therefore, it is inadmissible to simultaneously operate the gauge via
the RS232C Serial Interface and DeviceNet, Profibus, or the
The RS232C Serial Interface is used in duplex operation. The gauge continuously
(approximately every 20 ms) transmits a nine byte send string without request.
Instructions to the gauge are transmitted via five-byte receipt strings.
• binary
• 8 data bits
• 1 stop bit
• no parity bit
• no handshake
• 9600 Baud
• TxD Pin 13
• RxD Pin 14
• GND Pin 5
(sensor cable connector)
diagnostic port.
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1 Interface Protocol
1.1 Send String
Structure of send string
Status byte
(byte No. 2)
The complete send string (frame) is nine bytes (byte 0 … 8) long. Bytes 1 … 7 form
the data string.
Byte No. Function Value Comment
0 Data string length 7 Constant value
1 Page No. 4
2 Status
3 Error
4 Measured value high byte <value>
5 Measured value low byte <value>
Constant value for CDG025D1)
3
Constant value for CDGxxxD
2
Constant value for CDG025D 3)
→ "Status byte"
→ "Error byte"
→ "Calculation of pressure value"
→ "Calculation of pressure value"
2)
6 Read command <value> Read value
7 Sensor type
8 Checksum
1)
CDG025D with output signal 10.00 V (analog)
2)
CDG045D, CDG100D, CDG160D, CDG200D with output signal 10.24 V (analog)
3)
CDG025D with output signal 10.24 V (analog)
→ "Sensor type"
→ "Synchronization"
Bit 0 Definition
0 Continuous output of measured value
1 Individual measured value (polling) 1)
1)
→ 8, "DataTxMode". Send a read command of any parameter to the gauge for
requesting a send string.
Bit 2 Bit 1 Definition
1 0 Manual setpoint setting
1 1 Zero adjust active
Bit 3 Definition
0 ⇔ 1
Toggle bit, changes with every string
received correctly
Bit 5 Bit 4 Definition
0 0 Current pressure unit mbar
0 1 Current pressure unit Torr
1 0 Current pressure unit Pa
Bit 6 Definition
0 Standard measurement mode
1 Reserved for internal use
Bit 7 Definition
0 Heating
1)
1 Sensor temperature attained 1)
1)
for CDG045D, CDG100D, CDG160D, CDG200D only
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Error byte
(byte No. 3)
Error handling
Calculation of pressure value
Conversion formula
(byte No. 4 and 5)
Bit No. Definition
0 RS232 synchronization error
1 Incorrect command, e.g. inadmissible address (syntax error)
2 Inadmissible read command
3 SP1 status
4 SP2 status
5 Not used
6 Not used
7
Extended error set (→ Read command "Extended Error
L-Byte and H-Byte")
No bit set → value = 0x00 = no error set
Errors are only recorded in the error bytes as long as they persist, except for
RS232 interface errors. Errors are not acknowledged.
RS232 errors are signaled by the "toggle bit", i.e. when an RS232 error occurs, the
"toggle bit" is not inverted. For checking the status of the "toggle bit", a read
operation is required, which also allows to read the error byte for detailed error
analysis.
If an "extended error" is set, it has to be read as variable by means of the "read
command" (→ table "Variables for bytes No. 2 and 3"). After the read operation, the
variable is automatically erased.
The pressure is calculated from bytes 4 and 5 of the send string (decimal
presentation).
<pressure_value>×a
p =
b
×F.S.R._Mantissa×10
(F.S.R._Exp)
Parameter Description
p
Pressure value in selected pressure unit (→ Parameter a)
<pressure_value> Pressure measurement data, composed of "low and high
byte" (16 bit value) and converted into decimal format
F.S.R._Mantissa F.S.R. factor according to "Sensor type" variable, which
has to be read separately (→ "Read command")
F.S.R._Exp F.S.R. exponent according to "Sensor type" variable, which
has to be read separately (→ "Read command")
a Conversion factor for pressure units other than "Torr".
Torr: a = 1.00
mbar: a = 1.3332
Pa: a = 133.32
b Factor for resolution
Page No. 1) b Output signal
2 32000 10.24 V
3 32000 10.24 V
4 32767 10.00 V
1)
→ 3, tabel "Structure of send string", byte no. 1
4
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