Maple Systems OIT Family (ASCII) - Manual (Page 43)

Message Stacking
The OIT has two operating modes for screens requested by the ASCII host:
Standard Mode
Each screen request sent to the OIT is immediately displayed without regard to the message
currently on the display.
Note: If an alarm screen is currently displayed, screen requests from the ASCII host will be ignored
until the alarm is acknowledged or a higher priority alarm is requested by the ASCII host.
Stacked Mode
This mode is used if the OIT programmer wants to ensure that when the ASCII host displays a
screen on the OIT, the OIT operator sees it before another screen request overwrites the initial
request. Recall that in standard mode, each screen is immediately displayed when the ASCII
host sends a screen request to the Message Request Register or sends the Display Screen con-
trol command. This means that a screen may be displayed, but if the OIT operator is not in front
of the OIT and another screen is requested, the first screen will not be seen by the OIT operator.
When the OIT is operating in stacked mode, it keeps track of the last 10 screens requested by
the ASCII host. The stack operates in a First In First Out (FIFO) mode, that is the first mes-
sage placed onto the stack is the first message that is retrieved from the stack. In this fashion,
the OIT operator reads the messages in the order they were requested by the ASCII host. The
next message on the stack is displayed when the OIT operator presses the Next Message key
on the OIT. Messages programmed for timed display will be removed from the stack auto-
matically after being displayed for the programmed amount of time. Since the message stack
is only 10 messages deep, old messages fall off the stack as new messages arrive. As mes-
sages fall off, the screen on the display is updated.
If a message on the stack is chained to other messages, the OIT operator may press the Page
Up or Page Down keys to access the other messages within the chain.
42 OIT Family Operation Manual (ASCII)
1010-0088, REV02
Standard Mode
Screen Number
1 1st MESSAGE
Message
Last 10 Messages
can be reviewed
by pushing the
Last Message key.
A total of 10
messages can be
temporarily saved
in Standard Mode.
Next 10 messages
can be viewed
by pushing the
Next Message key.
Past messages can
also be reviewed
by pushing the
Last Message Key.
A total of 10 messages
can be temporarily saved
in Stacked Mode.
10 2nd MESSAGE
150 3rd MESSAGE
221 4th MESSAGE
52 5th MESSAGE
11 6th MESSAGE
25 7th MESSAGE
310 8th MESSAGE
300 9th MESSAGE
16 10th MESSAGE
77 PRESENT MESSAGE
Stacked Mode
Screen Number
1
1st MESSAGE
Message
10
2nd MESSAGE 150
3rd MESSAGE 221
4th MESSAGE 52
5th MESSAGE 11
6th MESSAGE 25
7th MESSAGE 310
8th MESSAGE 300
9th MESSAGE 16
10th MESSAGE 77
PRESENT MESSAGE