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READ_REG function block reads a register area from an addressed slave via Modbus Plus, TCP/IP-Ethernet or SY/MAX-Ethernet.
This function blocks use 1 data transaction path and require multiple cycles to complete an operation. Number of transaction path available is dependent on the communication port used:
- Modbus Plus embedded port or NOM modules support up to 4 blocks at the same time
- TCP/IP Ethernet embedded port support up to 4 blocks at the same time
- TCP/IP Ethernet NOE modules support up to 16 blocks at the same time
More communication function blocks may be programmed on the same communication port. However communication block exceeding the maximum number on that port will not be serviced until one of the transaction paths is freed up. When the transaction path resources become free the next block on the same port will become active and begin using freed path.
NOTE: Several copies of this function block can be used in the program. However, multiple instancing of these copies is not possible.