Delta RMC101 - Manual (Page 431)

Modbus Plus 5.3
Communications 5-181
When the master wishes to read from or write to a node it must take the following steps:
1. Wait for the token from the other nodes.
2. Send the request to the slave over the network to read or write data.
3. Give up the token.
4. Wait for the slave to receive the token and respond over the network.
Data Paths
This operation can take several milliseconds to complete, especially if many nodes are on the
network, which increases the token loop time. For this reason, Modicon allows several read and
write transactions to be in progress at a time. Each device has multiple data ”r;paths”. The RMC
has eight slave paths and therefore can handle eight simultaneous transactions. Most Modicon
PLCs have four master paths. The master (PLC) must specify the slave data path when reading
or writing data. This is described in greater detail in Using the MSTR Modicon Ladder Logic
Block.
Another method of speeding up the communication is to utilize Global Data. For details on this
feature, see Using Modbus Plus Global Data.
For details on reading and writing using a Modicon PLC, see Using the MSTR Modicon Ladder
Logic Block.
5.3.4 RMC Register Map (Modbus Plus)
Tip: RMCWin's Address Tool provides an easy way to identify addresses in the RMC. Simply open the
Address Tool and then move the cursor to any field in RMCWin that represents an RMC Register, and
the Address Tool will display the address in the address format of your choice. See Address Tool for
details.
The RMC module has 64K (65536) 16-bit registers that can be read from or written to over
Ethernet, Modbus Plus, and PROFIBUS-DP. Each register is assigned an address. However,
under the different communication methods, different addressing schemes are used. This topic
describes the addressing through Modbus Plus. For details on addressing from other modules
refer to the following topics:
• RMC Register Map (Allen-Bradley)
• RMC Register Map (Automation Direct)
• RMC Register Map (Modbus/TCP)