Maple Systems OIT Family (ASCII) User Manual

Page 15

higher priority alarm that has a continuous alert tone or shut down critical parts of the

system in case a hazardous potential exists. When the stack is no longer full, the OIT

clears the status coil.

Message Stack Full

The Message Stack Full status coil is set if the OIT’s internal message stack is full when the

message stack feature is being used. This feature allows the ASCII host to know that, al-

though it may have sent several messages to the OIT, nobody has read them yet. Therefore,

this status coil allows the ASCII host to take some sort of corrective action (such as sending

an alarm, or not sending any more messages until this coil is cleared by the OIT). When the

stack is no longer full, the OIT clears the status coil.

Message Stack Empty

The Message Stack Empty status coil is set by the OIT if the OIT’s internal message stack is

empty when the message stack feature is being used. This feature could allow the ASCII host to

send a burst of screen messages to the OIT, wait for the status coil to be set, then send another set

of screen messages. This offloads some of the overhead required by the ASCII host for interfac-

ing with the operator. When the stack is no longer empty, the OIT clears the status coil.

Clear Alarm

The Clear Alarm status coil is continuously monitored by the OIT (every 10 seconds) to allow

the ASCII host to clear the currently displayed alarm. If this bit is set by the ASCII host, the

OIT cancels any alarm that is in progress, and continues normal operation. Then the OIT clears

the status coil to indicate to the ASCII host that the action has been carried out. This feature

could be used to allow the ASCII host to cancel an alarm if the condition which caused the

alarm no longer exists. Care should be exercised when using this feature as the ASCII host does

not know which alarm it is clearing if multiple alarms have been stacked by the OIT, unless the

CMR is used (refer to the “Current Message Register” section).

Clear Alarm Stack

The Clear Alarm Stack status coil is similar to the Clear Alarm status coil except that this sta-

tus coil allows the ASCII host to clear the entire stack of alarms, including the currently dis-

played one. This feature could be used to cancel all existing alarms on the OIT if the ASCII

host performs a system-wide reset.

Note: Any alarms in the stack are automatically cleared whenever the OIT is reinitialized.

Alarm Stack Empty

The Alarm Stack Empty status coil is set by the OIT if the OIT’s internal alarm stack is empty.

This feature allows the ASCII host to know that the plant floor operator has acknowledged all

alarms that are currently active. Once all alarms have been acknowledged, the ASCII host may

go into a “normal” operating state. This coil is also set whenever the OIT initializes upon start-up.

When any alarms are received, the OIT clears this coil to indicate alarms are present.

Acknowledge Alarm

The Acknowledge Alarm status coil is set by the OIT if the operator presses the Alarm Ack key to

clear an alarm. This can be used to signal to the ASCII host that normal operation can begin

again.Itis the responsibility ofthe ASCIIhost to clear this coil once ithas been set by the OIT.

OIT Family Operation Manual (ASCII)

1010-0088, REV02