Vaisala DPT146 - Manual (Page 54)

User's Guide _______________________________________________________________________
52 ___________________________________________________________________ M211372EN-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 10 below to configure the Modbus RTU using
the USB service cable.
Table 10 Configuration commands for Modbus RTU
Service Command Description
SMODE MODBUS Enable Modbus communication protocol
See section Set Serial Line Operating Mode on page
47.
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 48.
ADDR a Set Modbus address
a = new address (0…255)**
See section Set Transmitter Address on page 48.
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 49.
* 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 DPT146 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.