施耐德勾选 “启用编程协议”后，可使用502端口90功能码编程。
1和2功能码可用来转发%M内部位寄存器
3和4功能码可用来转发%MW字寄存器
把%I0寄存器映射到%MW0
把%Q0寄存器映射到%MW1
参考资料：
https://www.se.com/my/en/faqs/FA308725/
How can I read %I/Q or %M on my M221 M241 M251 M258 LMC058 using Modbus ?
Published date: 25 January 2018
2 cases have to be considered: M221 or (M241 M251 M258 LMC058).
M221 :
%M (internal bits) can be accessed using function codes from the table below (extracted from SoMachine Basic online help).
Note that %I (physical inputs) and %Q (physical outputs) can not be accessed directly by Modbus.
M241 M251 M258 LMC058:
%M (internal bits) cannot be accessed by Modbus.
But %I (physical inputs) and %Q (physical outputs) can be accessed using function codes from the table below (extracted from SoMachine online help).
