IBM Modbus Plus manual Source Accesses

Mappings

4.2 Source Accesses

The Modbus Plus driver supports four possible source accesses.

The first source defines a local address which allows any device on the Modbus Plus network to write the data to the X-Link. This type of source is ideal for data that changes infrequently, but must be forwarded immediately, such as errors or exceptions. Programming must be provided on the remote device to update the data when necessary.

The second type of source supported by the Modbus Plus driver is an X-Link initiated read. This source defines an external address which the X-Link uses to read the data from a remote node on the network. This access also requires you to specify when to read the data. This type of data source does not require any programming in the remote node, but generates extra network bandwidth to poll the data.

The next source is Modbus Plus global data. As each station passes data on the network, it has the opportunity to transmit up to 32 integers to all the other stations on the network. This global data can be accessed as a source for an X-Link mapping. To access global data, you provide a station address (1 to 64) and an offset into that station's global data table.

The last source is Modbus Plus network statistic counters. To access the counters stored on the SA85 card, provide an offset specifying the number of words to skip from the beginning of the diagnostic counters.

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