2 Operation PLC Memory Area Access The supported Modbus function codes allow access to the PLC memory areas as shown. Bit (Coil) Read/Write All supported Bit (Coil) read/write operations access the CIO memory area from CI O 1000 to CIO 1199. This provides a total of 3200 coils for access from the Modbus master device. These function codes include: • 01, Read Coil Status • 02, Read Input Status • 05, Write Single Coil • 0F, Write Multiple Coils Channel (Register) Read/Write All supported Channel (Register) read/write commands access the DM memory area from D1000 to D1199. This provides a total of 200 registers to be accessed from the Modbus master device. These function codes include:
• 03, Read Holding Registers • 04, Read Input Registers • 06, Preset Single Register • 10, Preset Multiple Registers Modbus Addressing When addressing the PLC memory map using the Modbus TCP protocol, D1000 is considered the first register and CIO 1000.00 is considered the first coil. Channel (Register) Calculation Example To determine the Modbus TCP register number for a PLC address, simply subtract 1000 from the PLC Data Memory location as shown in the examples below.
2-10 Grid Connect Modbus/TCP Adapter Application and Setup Guide PLC Memory Location Calculation Modbus Register D1000 (D)1000 - 1000 = 0 0 D1050 (D)1050 - 1000 = 50 50 D1099 (D)1099 - 1000 = 99 99 D1199 (D)1199 - 1000 = 199 199