Maple Systems OIT Family (ASCII) - Manual (Page 44)

When message stacking is enabled, some OIT’s have a Message Stack LED which lights up
to indicate a message is in the message queue. The OIT can also display the current number
of messages in the message stack on any screen through the use of the Message Stack Moni-
tor. The Message Stack Monitor requires two character spaces on the screen and is placed us-
ing the Register Monitor Editor in the OITware 200 configuration software.
Note: Stacked Mode is not available on the OIT3160 and OIT4160 models.
How Screens are Displayed
The OIT Family Operator Interface Terminals offer many ways to display stored screens.
Once the screens have been created and stored in the OIT, they can be shown on the OIT’s
display in the following ways:
Startup Screen
Any message, recipe, or menu screen created can be identified as a startup screen. Once des-
ignated, the startup screen will automatically appear on the OIT display whenever the OIT is
powered up.
ASCII Host Request
The ASCII host can display a screen on the OIT in two ways: by using the Display Screen
control command or by using the Write OIT Memory control command to place the screen
number in the Message Request Register (MRR). The OIT reads the MRR every 200ms. The
OIT can be programmed to interpret the number in the MRR as either a binary decimal, or
BCD number. When the ASCII host places a screen number in the MRR, the OIT displays
that screen and performs any special functions required by the display screen’s contents (for
example, sound buzzer). The actual OIT data register used as the MRR is selected during
OIT configuration (refer to the Configuration Editor in the OITware 200 User’s Guide).
In addition to the Message Request Register, the OIT has a Current Message Register (CMR)
that is used to convey to the ASCII host the number of the current screen displayed. This reg-
ister is optional and can be disabled if not required.
For more information on how the MRR and CMR operate, refer to the Message Request Reg-
ister and Current Message Register sections in the Operation chapter.
Function Key
Every function key on the OIT can be programmed to display one screen when the function
key coil is set and a different screen when the function key coil is cleared. Whenever the
function key is pressed, the corresponding screen is immediately displayed, unless an alarm
is active or a security password is being used.
Note: If a function key is configured to display a help screen or alarm screen, these screens
will be treated by the OIT as normal message screens.
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