Vaisala DPT145 - Manual (Page 46)

User's Guide _______________________________________________________________________
46 ___________________________________________________________________ M211371EN-D
Configuration Commands Related to Modbus
In addition to enabling the Modbus protocol in the device, Modbus over
RS-485 needs the following software settings: serial bit rate, parity,
number of stop bits, and Modbus device address.
Use the service commands listed in Table 9 below to configure the
Modbus RTU using the USB service cable.
Table 9 Configuration commands for Modbus RTU
Service Command Description
SMODE MODBUS Enable Modbus communication protocol.
See section Set Serial Line Operating Mode on page
41.
SERI b p 8 s Change baud rate and parity.
b = baud rate (minimum 9600 when using Modbus)
p = parity (E, N, or O)
8 = number of data bits must be 8
s = number of stop bits (2 if parity is N, 1 otherwise*)
See section Set Serial Line Settings on page 42.
ADDR a Set Modbus address.
a = new address (0…255)**
See section Set Transmitter Address on page 42.
SDELAY d Add extra Modbus response delay.***
d = new delay in units of 1/250 seconds (0…255)
See section Set Serial Line Response Time on page 43.
* Modbus specification defines that two stop bits must be used if parity is N.
** Setting address to zero switches the instrument offline from the Modbus bus.
Addresses 248 … 255 are not supported by the Modbus standard but DPT145 works
with them.
*** Extra response delay can be used, for example, to avoid problems caused by
direction-switching delays in bus converters.
NOTE The instrument must be switched off and on before the configuration
changes made with the service cable take effect.