OIT Family
(Operational Overview)

The OIT Family operator interface terminals communicate with PLCs and Motion Controllers by using point-to-point serial communications to read from and write to the internal discrete and register memory of the controller. Some of the controller's discrete and register memory is designated for special purposes: Message Request Register, Current Message Register, Status Bit Coils and Key Coils.

Message Request Register

The Message Request Register (MRR) is a register in the controller that is continuously monitored by the OIT. When the controller enters a number into this register, the OIT:
displays the screen that corresponds to that number
performs any special functions associated with the screen
and optionally sends the screen's contents to a serial printer.

For example, the system programmer may want Screen #30 to be shown on the OIT whenever input coil X1 is turned on. Screen #30 might say "Oven Door is Open!!!". The relay ladder logic could be the following:

In this case, D500 is the MRR that the OIT has been configured to poll once every 200 milliseconds. When input coil X1 is activated, the controller puts the decimal number 30 into the MRR. The OIT then sees the number 30 in the MRR and displays Screen #30.

Current Message Register

The OIT can be programmed to send the number representing the screen currently displayed on the OIT to a register in the controller called the Current Message Register (CMR). The CMR can be used by the controller to determine which screen is currently being displayed on the OIT. This might be used to determine which screen in a chained sequence the OIT operator is currently seeing.

Status Bit Coils

The Status Bit coils are a block of discrete coils in the controller that are used by the OIT to communicate information to the controller.

• Message Received is set by the OIT when a screen request has been successfully retrieved from the controller.
• Invalid Display Message Number is set by the OIT when the controller requests an empty or non-existent screen.
• Message/Keytable Error is set by the OIT when it detects invalid or corrupted data in the screens or keytable.
• Message Stack Full and Message Stack Empty are set when the screen stack feature is enabled and the OIT's internal screen stack is full or empty.
• Reset is set by the OIT each time it powers up or performs a re-initialization due to exiting the OIT's local setup menu.
• Alarm Stack Full and Alarm Stack Empty are set by the OIT when the OIT's internal alarm stack is full or empty.
• Clear Alarm is monitored by the OIT to allow the controller to clear the currently displayed alarm. When the controller sets this coil the OIT cancels the alarm in progress.
• Clear Alarm Stack is monitored by the OIT to allow the controller to clear the entire stack of alarms, including the alarm in progress.
• Acknowledge Alarm is set by the OIT when the operator presses the Alarm Ack key to clear an alarm.
• OIT Pulse is pulsed by the OIT every 10 seconds. This allows the controller to determine if the OIT is still communicating with it.
• Update PLC Clock is set by the OIT when the OIT starts sending new time and date information to the controller and cleared by the OIT when the OIT is finished.

Key Coils

The Key Coils are divided into two blocks of discrete coils in the controller: Function Key Coils and Control Key Coils. The Key Coils are used to pass keypress data from the OIT to the controller. When a key is pressed, the corresponding coil in the controller is activated. For example, the system programmer wants a motor to run whenever the F1 function key is being pressed by the operator. The relay ladder logic could be:

In this case, internal control relay C389 has been configured as the Function Key Coil for the F1 function key. If the F1 function key has been configured as momentary, then C389 will be activated as long as the F1 function key is being pressed by the operator. Internal control relay C389 is controlling output coil Y33, which is controlling a motor. Consequently, the motor runs whenever the operator is pressing the F1 function key.

Register Monitoring

Set Points
Set points are controller memory locations that the OIT monitors. Up to 16 can be active simultaneously. Each set point is configured with a controller memory address to monitor, a low and high limit, and OIT screen numbers to display upon low or high limit violation. Set points have a variety of uses: system warnings or alarms, restarting a recipe after a given number of units have been batch processed, or providing the operator with a choice of actions when a trip point has been exceeded.

Linear Scaling
Programmable linear scaling is available on the signed, decimal and long register monitor formats. Linear scaling is the process of converting one unit of measure to another, usually from a machine format to an operator-readable format, so the operator has the data presented in readily understandable terms. A common application involves converting analog or digital data into degrees, speed, voltage or temperature. If linear scaling is used on a read/write register, the operator can modify the data in the operator-readable format and it will be converted back into the machine format before being sent to the controller.