Xeo4 RILHEVA II, User Manual

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In order to calculate the Rb resistor value, we have to bear in mind that they must maintain a
voltage of about 200 mV when all the devices are listening.
Let’s do an example on how to find the Rb resistance value.
We suppose to be in the following situation:
•
The bus is composed by 32 nodes with input impedance equal to 12KΩ
•
Two termination resistors (120Ω) are present
•
Supply voltage is 5 VDC
We say Zo the impedance made by the parallel of 2 termination resistors (120Ω) and 32 input impedance of
the devices (12kΩ), whose result is about 52Ω;
and we say E the power voltage for the bus polarization (5V)
Rb is calculated by the following formula:
In this case the value is about 620 Ω.
This polarization network must be connected in a single point of the bus, possibly close to the master
device (Rilheva II).