MAN0964-14-EN_XL4_XL4P_UM
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Polled Read/Write/Init
On every transaction scan, a read target device register transaction occurs unless a local
register value has changed. The write transaction only updates those local registers that have
changed in value. If several non-consecutive local registers (contained in a single mapping
entry) change value between transaction scans, it takes several consecutive scans to write
each changed register.
When the OCS is placed in RUN mode, the initial action for this mapping type is a write target
register transaction. This transaction initializes the target device register(s) to match that of
the local (OCS) register(s). Thereafter, any change to the corresponding OCS register(s)
triggers a write operation to the remote device.
The initial write transaction does not occur until after the first logic scan of the OCS. This
allows registers to be initialized locally before Writing to the target device register(s).
Triggered Read
A read transaction is triggered by a high level on a separately designated OCS (binary) trigger
register. Once the read transaction is complete (or the device is offline), the OCS trigger
register is cleared by the OCS. This update type can be used for occasion data accesses such
as retrieving trend data.
NOTE: This operation increases the associated transaction scan time and can cause the
Update Interval Exceeded Counter to increment on a tightly adjusted update interval.
Triggered Write
A write transaction is triggered by a high level on a separately designated OCS (binary)
trigger register. Once the write transaction is complete (or the device is offline), the OCS
trigger register is cleared by OCS. This function can be used for occasion data accesses such
as sending recipe data.
NOTE: This operation increases the associated transaction scan time and can cause the
Update Interval Time Exceeded Counter to increment on a tightly adjusted update interval.
