Cutler-Hammer D320 PLC, User Manual

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Appendix C: COM2 UDCP Specification
235
Description of Operation – MODBUS RTU mode
When configured for operation as a MODBUS RTU slave (by setting the Enable MODBUS Flag
F12.9), the D320 communication port supports the open standard MODBUS RTU slave instructions
shown in Table 4 below.
Table 4 – Supported MODBUS RTU Slave Commands
Command Code (Hex) Description
Read Coil 01 Read ON/OFF status of logic coil(s)
Read Input 02 Read ON/OFF status of discrete input(s)
Read Holding Register 03 Read value of internal register(s)
Read Input Register 04 Read value of input register(s)
Write Coil 05 Write single logic coil to ON/OFF
Write Register 06 Write value into single internal register
Read Exception 07 Read internal status register (special)
Write Multiple Coils 15 Write multiple logic coils to ON/OFF
Write Multiple Registers 16 Write values into multiple internal registers
Report Slave ID 17 Report Slave node address on network
MODBUS Memory Mapping
When a D320 responds to a MODBUS RTU master message to read or write a coil or register, the
address contained in the MODBUS message is directly mapped to the absolute memory address in the
D320 PLC. No distinction is made between the memory location of coils, inputs, holding registers, or
input registers with regard to the address being requested. For example, a MODBUS Read Coil request
from address 0 will reply with a single bit from D320 absolute address 0, and the value of contact R0.0
will be returned. Likewise, a MODBUS Read Holding Register request for 3 registers, starting at
address 512, will return the values of D320 memory locations W0, W1, and W2. See Chapter 5 and
Table 5 below for a listing of the absolute addresses of the memory locations in the D320 CPU.
Table 5 – Absolute Memory Addresses
Absolute Address
Memory Type Register Addresses
Decimal Hexadecimal
External I/O R000 – R127 0 – 127 0000 – 007F
Link Network Relays L000 – L063 128 – 191 0080 – 00BF
Internal Contacts M000 – M127 192 – 319 00C0 – 013F
Internal Keep Contacts K000 – K127 320 – 447 0140 – 01BF
System Flags F000 – F015 448 – 463 01C0 – 01CF
Data Registers W0000 – W2047 512 – 2559 0200 – 09FF
T/C Set Value SV000 – SV255 2560 – 2815 0A00 – 0AFF
T/C Present Value PV000 – PV255 2816 – 3071 0B00 – 0BFF
System Registers SR000 – SR511 3072 – 3583 0C00 – 0DFF