The response message is transmitted to the master. ( B

half the scan time.
The time allotted for servicing Modbus ports at the end of the controller scan (before beginning
a new scan) depends upon the controller model. Timing for each model is described on the next
page.
For 484 controllers the time is approximately 1.5 ms. The Modbus port is available on a
contention basis with any J470 / J474 / J475 that is present.
For 584 and 984 controllers the time is approximately 1.5 ms for each Modbus port. The ports
are serviced sequentially, starting with port 1.
For 184 / 384 controllers the time varies according to the amount of data being handled. It
ranges from a minimum of 0.5 ms to a maximum of about 6.0 ms (for 100 registers), or 7.0 ms
(for 800 coils). If a programming panel is currently being used with the controller, the Modbus
port is locked out.
D Modbus functions 1 through 4, 15, and 16 permit the master to request more data than can be
processed during the time alloted for servicing the slave's Modbus port. If the slave cannot
process all of the data, it will buffer the data and process it at the end of subsequent scans.
The amount of data that can be processed during one service period at the Modbus port is as
follows:
Note: 984-X8X refers to 984 slot mount models (984-385, -685, etc).
For the 884, the processing time for multiple data is as follows:
E LRC calculation time is less than 1 ms. CRC calculation time is about 0.3 ms for each eight
bits of data to be returned in the response.
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