Chapter 4 _________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 37
Modbus Communication
The Modbus variant used in HMP60 and HMP110 series probes is
Modbus RTU. For a list of the available Modbus registers, see Appendix
A, Modbus Reference on page 75. The default communication settings
used when Modbus is enabled at the factory (chosen when ordering) are
listed in Table 9 below.
Table 9
Default Modbus Communication Settings
Setting
Default value (when Modbus is
enabled at the factory)
Device address
240
Bit rate
19200
Number of data bits
8
Parity
N
Number of stop bits
2
Response delay
0
Communication mode MODBUS
The communication settings can be changed with either serial line
commands (see Table 10 below) or with the related Modbus
configuration registers (see Table 18 on page 76).
If the device is already in Modbus mode, open the serial line interface as
instructed in Accessing Serial Line Command Interface (RS-485 Mode)
from Analog or Modbus Mode on page 36.
Table 10
Serial Line Configuration Commands for Modbus
RTU
Serial Command Description
SMODE MODBUS
Enable Modbus communication protocol
SERI b p 8 s
Change baud rate and parity
b = baud rate (9600, 19200, 38400, 57600)
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*)
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 with
HMP 60 and HMP110 series. Address 0 cannot be used on Modbus.
*** 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 communication
setting changes take effect.
