Teledyne gfc 7000ta 7. I2C Data Bus, Status Outputs, Control Inputs, Power up Circuit

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer

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. I2C Data Bus

An I2C data bus is used to communicate data and commands between the CPU and the touchscreen/display interface and the relay board. I2C 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 I2C. 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 I2C 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 I2C circuitry to specific values until the CPU boots and the instrument software can establish control.

Teledyne Analytical Instruments 210