# Modbus Query ## Modbus query command ``` [[Modbus query 1],[Modbus query 2],.....] ``` ## Things required to make Modbus query * Slave ID * Function code * Starting address * How many registers/coils want to be read * Data type * Index ## Modbus query format \[ Slave ID, Function code, Starting address, No. of registers/coils want to read, Data type, Index] ## How to choose function code It depends on starting address of the register or coil. | Parameter | Register / Coil Address | Function Code | | ---------------------- | ----------------------- | ------------- | | Coil status | 00001 on words | 1 | | Input Coil status | 10001 on words | 2 | | Holding register | 40001 on words | 3 | | Input holding register | 30001 on words | 4 | ## How to choose starting address & number of registers
* For eg: if we want to read the parameters like `Watts Total`, `Watts R phase`, `Watts Y phase`, `Watts B phase`, and `VAR Total` from the Elmeasure `EN8400` Energy meter then its address is from 40101 to 40110. so now the starting address would be 100 & no. of registers want to read would be 10. * `NOTE: The number of register would be 2 in order to read single parameter of data type float, UINT32, INT32 & for rest it would be 1.` ## How to choose the data type * Supported data types & formats are: | Datatypes case no | Datatype | Remark | | ----------------- | ---------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | 0 | Float ABCD | | | 1 | Float DCBA | | | 2 | Float BADC | | | 3 | Float CDAB | Generally, the datatype mentioned in the datasheet will be without data format\[A, B, C, D sequence], for example, `datatype is float`. In that case, use this format\[default]. | | 4 | UINT ABCD | | | 5 | UNIT DCBA | | | 6 | UINT BADC | | | 7 | UINT CDAB | Generally, the datatype mentioned in the datasheet will be without data format\[A, B, C, D sequence], for example, `datatype is UINT32`. In that case, use this format\[default]. | | 8 | INT ABCD | | | 9 | INT DCBA | | | 10 | INT BADC | | | 11 | INT CDAB | Generally, the datatype mentioned in the datasheet will be without data format\[A, B, C, D sequence], for example, `datatype is INT32`. In that case, use this format\[default]. | | 12 | INT AB | Generally, the datatype mentioned in the datasheet will be without data format\[A, B sequence], for example, `datatype is INT16`. In that case, use this format\[default]. | | 13 | INT BA | | | 14 | UINT AB | Generally, the datatype mentioned in the datasheet will be without data format\[A, B sequence], for example, `datatype is UINT16`. In that case, use this format\[default]. | | 15 | UINT BA | | * In case of Coil status or input Coil status data type is not mandatory, we can choose default data type 0. * `Note: In some exceptional cases even after selecting the [default] data format, we will observe that we are not receiving data from the slave in that scenario we have to do a trial & error by selecting a different data format until we will receive the data`. ## Index Index number is nothing but a number of queries you have? The first query index is 0. ### Example Queries #### Schneider meter EM6436 UART: `{"action":"modbus", "mb_mode":"1", "baud":"4800", "data_bits":"8", "parity":"EVEN", "stop_bits":"1", "mb_interval":"2000", "mb_timeout":"1000"}` `[[1,3,3000,20,3,0], [1,3,3030,20,3,1], [1,3,3060,20,3,2], [1,3,3090,20,3,3], [1,3,3120,4,3,4], [1,3,3150,4,3,5]]`