MAN0974-14-EN_XL7_XL7P_UM
July 6, 2022
Page 131 | 199
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.
