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FS-8700-01 Modbus RTU/ASCIIFS-8700-01_Modbus_RTU Driver Manual Page 17 of 22
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Appendix B. Useful Features
Appendix B.1. Map Descriptor Functions
Function Description
Rdbc
This is an active Map Descriptor which polls the device once every scan interval. The function will also
execute writes from the Data Array to a remote device when a change is detected, but only when
used in conjunction with writeable addresses.
Arco
The Arco function is the same as Rdbc except that the length of the Map Descriptor is taken as the
number of zones to poll. The start zone number is specified under the Zone Map Descriptor field.
More than one Arco Map Descriptor may be used to poll two series of zone numbers, eg. from 5-10
and from 300-340. Arco Map Descriptors with Length 1 perform the same function as Rdbc Map
Descriptors with the same length.
Arcs
This function will perform the same operation as an Rdbc (Arc) function, but will sequence through
the range of addresses starting at "Address" and wrapping at "A Length". A length of 1 will be
used for every one of the Addresses that gets polled.
Wrbx
The Wrbx function will write data from the Data Array to the remote device. The write is triggered by
a change in the associated Data Array. If the associated Data Array is updated a write will occur, even
if the value/s within the Data Array have not changed. The “Scan_Interval” parameter is not required
for this function as writes are event driven and not continuous
Wrbc
This is similar to the Wrbx function, except that the writes occur at a regular interval rather than on
an event driven basis. The frequency of the writes is determined by the “Scan_Interval” parameter.