This function code is used by TOP Server when requesting a read of one or more (up to 125 at a time) holding registers or 4xxxxx type analog addresses. Input coils are read-only in a Modbus device, so you'll notice there is no function code designated for writing to a 1xxxxx type address. This function code is used by TOP Server when requesting a read of one of more (up to 2000 at a time) input coils or 1xxxxx type discrete/boolean addresses. Output coils are read/write access - you'll see support for Function Codes 5 and 15 a further down the list. This function code is used by TOP Server when requesting a read of one or more (up to 2000 at a time) output coils or 0xxxxx type discrete/boolean addresses. Let's discuss each function code and the corresponding address and function it performs: ![]() So, since we're talking in more depth about Modbus function codes, it is essential that we talk about Modbus addresses in terms of the type of memory a particular address is and whether or not it can be read from and written to or only read from.īoth of those factors determine which Modbus function code will be used in sending a request to a device. We also discussed last time how a lot of device documentation doesn't always provide detailed listings of Modbus addresses in terms of the type of address such as 4xxxxx or Holding Register.
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