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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. |
