可能是你查的资料不全面，或协议版本不同
功能码22:Mask Write 4X Register
Modifies the contents of a specified 4XXXX register using a combination of an AND mask, an OR mask,
and the register’s current contents. The function can be used to set or clear individual bits in
the register. Broadcast is not supported.
This function is supported in the 984–785 controller only.
比如本站讨论过的用异或实现单键起停的技巧，如果用通讯实现就可以用这个功能码
功能码23：Read/Write 4X Registers
Performs a combination of one read and one write operation in a single modbus transaction.
The function can write new contents to a group of 4XXXX registers,
and then return the contents of another group of 4XXXX registers. Broadcast is not supported.
This function is supported in the 984–785 controller only.
用一条帧同时操作多个寄存器（不同于操作连续寄存器的功能码3、16）