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modbus_rtu_set_rts() modbus_rtu_set_rts() Name modbus_rtu_set_rts - set the RTS mode in RTU Synopsis int modbus_rtu_set_rts(modbus_t *ctx, int mode) Description The modbus_rtu_set_rts() function shall set the Request To Send mode to communicate on a RS-485 serial bus. By default, the mode is set to MOD- BUS_RTU_RTS_NONE and no signal is issued before writing data on the wire. To enable the RTS mode, the values MODBUS_RTU_RTS_UP or MOD- BUS_RTU_RTS_DOWN must be used, these modes enable the RTS mode and set the polarity at the same time. When MODBUS_RTU_RTS_UP is used, an ioctl call is made with RTS flag enabled then data is written on the bus af- ter a delay of 1 ms, then another ioctl call is made with the RTS flag disabled and again a delay of 1 ms occurs. The MODBUS_RTU_RTS_DOWN mode applies the same procedure but with an inverted RTS flag. This function can only be used with a context using a RTU backend. Return value The function shall return 0 if successful. Otherwise it shall return -1 and set errno to one of the values defined below. Errors • EINVAL, the libmodbus backend isn't RTU or the mode given in argument is invalid. Example Enable the RTS mode with positive polarity: modbus_t *ctx; uint16_t tab_reg[10]; ctx = modbus_new_rtu("/dev/ttyS0", 115200, 'N', 8, 1); modbus_set_slave(ctx, 1); modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485); modbus_rtu_set_rts(ctx, MODBUS_RTU_RTS_UP); if (modbus_connect(ctx) == -1) { fprintf(stderr, "Connection failed: %s\n", modbus_strerror(errno)); modbus_free(ctx); return -1; } rc = modbus_read_registers(ctx, 0, 7, tab_reg); if (rc == -1) { fprintf(stderr, "%s\n", modbus_strerror(errno)); return -1; } modbus_close(ctx); modbus_free(ctx); See also • modbus_rtu_get_rts <modbus_rtu_get_rts.md> modbus_rtu_set_rts()
Name | Synopsis | Description | Return value | Errors | Example | See also
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