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modbus_receive() modbus_receive() Name modbus_receive - receive an indication request Synopsis int modbus_receive(modbus_t *ctx, uint8_t *req); Description The modbus_receive() function shall receive an indication request from the socket of the context ctx. This function is used by a Modbus slave/server to receive and analyze indication request sent by the masters/clients. If you need to use another socket or file descriptor than the one defined in the context ctx, see the function modbus_set_socket <mod- bus_set_socket.md>. Return value The function shall store the indication request in req and return the re- quest length if successful. The returned request length can be zero if the indication request is ignored (eg. a query for another slave in RTU mode). Otherwise it shall return -1 and set errno. Buffer size The maximum size of the request depends on the used backend, in RTU the req array must be MODBUS_RTU_MAX_ADU_LENGTH bytes and in TCP it must be MOD- BUS_TCP_MAX_ADU_LENGTH bytes. If you want to write code compatible with both, you can use the constant MODBUS_MAX_ADU_LENGTH (maximum value of all libmodbus backends). Take care to allocate enough memory to store requests to avoid crashes of your server. Example uint8_t req[MODBUS_MAX_ADU_LENGTH]; rc = modbus_receive(ctx, req); See also * modbus_set_socket <modbus_set_socket.md> * modbus_reply <modbus_reply.md> modbus_receive()
Name | Synopsis | Description | Return value | Buffer size | Example | See also
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