Maple Systems OIT Family - Manual (Page 65)

CHAPTER 5
Displaying Stored Screens
This chapter describes the methods that can be used to display stored screens on the OIT.
Startup Screen
One message, recipe, or menu screen can be designated as the startup screen. The startup screen
automatically appears whenever the OIT is powered up. For instructions on designating the
startup screen, refer to the Startup Screen section in CHAPTER 3: Stored Screens.
PLC Screen Request
The PLC can request that the OIT display any stored screen using the Message Request
Register (MRR). The MRR is a register in the PLC that is continuously monitored by the OIT.
When a new value is read from the MRR, the corresponding screen is immediately displayed
on the OIT with the following exceptions:
• When the screen stack is in Stacked mode, only alarm screens are immediately displayed, all
other screens arestored inthe stackuntilthe OIToperator presses the NEXT MESSAGEkey.
• The only screen request that can write over the top of an unacknowledged alarm screen is a
higher priority alarm screen. Non-alarm screen requests received in this situation are
ignored if the screen stack is in Standard mode and saved in the stack if the screen stack is
in Stacked mode. Lower priority alarm screens received in this situation are stored in the
alarm stack.
Once the OIT displays the screen requested in the MRR, the OIT must see a change in
the number in the MRR in order to display another screen request from the PLC. For
example, the PLC requests that Screen #5 be displayed. The OIT operator then presses
Function Key #1 which displays Screen #30. The number 5 is still in the MRR, but since
no change has occurred it is ignored by the OIT. The PLC can get the OIT to display the
same screen twice without an intervening PLC screen request, by simply putting the
number 0 into the MRR between the two identical screen requests. The OIT does not
perform any action as a result of seeing the number 0 in the MRR, but it does note that a
change occurred.
NOTE:The OIT3100 and OIT4100 Series offers a feature that allows the OIT to clear the MRR
after each PLC screen request.
Two types of MRRs are available: Value and Bit Position.
MRR–Value
When a value MRR is used, the PLC requests screens by placing decimal or BCD
numbers into the MRR.
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