Chapter 4 _________________________________________________________________ OperationVAISALA ________________________________________________________________________ 35Modbus CommunicationThe Modbus variant used in HMP60 and HMP110 series probes isModbus RTU. For a list of the available Modbus registers, see AppendixA, Modbus Reference on page 73. The default communication settingsused when Modbus is enabled at the factory (chosen when ordering) arelisted in Table 8 below.Table 8 Default Modbus Communication SettingsSetting Default value (when Modbus isenabled at the factory)Device address 240Bit rate 19200Number of data bits 8Parity NNumber of stop bits 2Response delay 0Communication mode MODBUSThe communication settings can be changed with either serial linecommands (see Table 9 below) or with the related Modbus configurationregisters (see Table 17 on page 74).If the device is already in Modbus mode, open the serial line interface asinstructed in Accessing Serial Line Command Interface (RS-485 Mode)from Analog or Modbus Mode on page 34.Table 9 Configuration Commands for Modbus RTUSerial Command DescriptionSMODE MODBUS Enable Modbus communication protocolSERI b p 8 s Change baud rate and parityb = baud rate (9600, 19200, 38400, 57600)p = parity (E, N, or O)8 = number of data bits must be 8s = number of stop bits (2 if parity is N, 1 otherwise*)Bit rates less than 9600 b/s are not supported with Modbus.ADDR a Set Modbus address: a = new address (1…247)**SDELAY d Add extra Modbus response delay***d = new delay in units of 1/250 seconds (0…255)* Modbus specification defines that two stop bits must be used if parity is N.** Addresses 248 … 255 are not supported by the Modbus standard but work withHMP 60 and HMP110 series. Address 0 cannot be used on Modbus.*** Extra response delay can be used, for example, to avoid problems caused bydirection-switching delays in bus converters.NOTE The instrument must be switched off and on before the communicationsetting changes take effect.
