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Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 210
9.3.6.6. External Digital I/O
This External Digital I/O performs two functions: status outputs and control inputs.
Status Outputs
Logic-Level voltages are output through an optically isolated 8-pin connector located on the rear panel of
the analyzer. These outputs convey good/bad and on/off information about certain analyzer conditions.
They can be used to interface with certain types of programmable devices (See Section 6.13.1.1).
Control Inputs
By applying +5VDC power supplied from an external source such as a PLC or Data logger (See Section
6.13.1.2), Zero and Span calibrations can be initiated by contact closures on the rear panel.
9.3.7. I
2
C Data Bus
An I
2
C data bus is used to communicate data and commands between the CPU and the
touchscreen/display interface and the relay board. I
2
C is a two-wire, clocked, digital serial I/O bus that is
used widely in commercial and consumer electronic systems. A transceiver on the motherboard converts
data and control signals from the PC-104 bus to I
2
C. The data is then fed to the touchscreen/display
interface and finally onto the relay board.
Interface circuits on the touchscreen/display interface and relay boards convert the I
2
C data to parallel
inputs and outputs. An additional, interrupt line from the touchscreen to the motherboard allows the CPU
to recognize and service button presses on the touchscreen.
Power up Circuit
This circuit monitors the +5V power supply during start-up and sets the Analog outputs, external digital
I/O ports, and I
2
C circuitry to specific values until the CPU boots and the instrument software can
establish control.