iSMA-B-MINI/MIX Modbus User Manual
www.ismacontrolli.com
DMP262en | 1st Issue rev. 8 | 05/2022
page 36 of 107
Value
No. of Stop Bits
256
RS485 biasing*
Table 11. Stop bits
* Bit No. 8 activates RS485 biasing resistors in order to pull-up the voltage on the RS485
bus. If the bit no. 8 is true (bit 8 = 1), RS485 biasing resistors are activated. The function is
only
available in
MINI IP I/O modules
with hardware version >= 2.0
The biasing resistors are useful in case the iSMA modules are connected with third-party
devices with the same RS485 bus and communication errors appear on the network.
Figure 39. Modbus frame
6.13 Data Bits (40138)
The number of data bits transmitted in a single byte is determined according to the
following table:
Value
No. of Data Bits
7
7
8 (default)
8
Table 12. Data bits
6.14 Parity Bit (40139)
Every byte of data being transferred may have additional protection in the form of a parity
bit added before the stop bit (bits).
The method of calculating the parity bit is presented in the table below:
Register Value
Type of Parity Bit
0 (default)
None
1
Odd (number of all ones in a byte is odd)
2
Even (number of all ones in a byte is even)
WARNING!
Only a single device in the network can have biasing resistors activated!