Global data can be either output data or input data. Global output is identical to a MSTR block global write function. A PLC or PC with a Modbus Plus adapter, configured for global output, can send up 32 words ( registers, or 16 bits of discrete information ) to all nodes. The data is sent with each token pass and is picked up by the nodes configured for global input. Nodes configured for global input can request up to 32 words from each node up to a maximum of 500 words. The data may be placed in any part of state ram..
Specific data is sent as a specific output and received as a specific input. The output data is sent to a particular node on the network. A PLC or PC with a Modbus Plus adapter can send up to 32 words per node up to a maximum of 500 words. The data can come from anywhere in state ram, but it must be contiguous. Specific input must be configured on the node receiving the specific output data. A Modbus Plus node can receive up to 32 words from each node up to a maximum of 500 words..