SLLU376 December 2023
The differential side of the RS-485 transceiver also has a few minor modifications that can be made. Both differential buses on the EVM have 0805 pads for a termination resistance and a termination capacitance to be added to test multiple configurations of the RS-485 or RS-422 bus. The other modification is by applying a common mode voltage through the common mode jumpers J6 through J8 for the differential input pair, A and B pins, which is connected to the main bus through the common mode loading resistors R22 and R23 and, by default, are not installed. The same common mode loading scheme is allowed for the Y and Z pins as well trough jumpers J15-J17 with common mode loading resistor pads R24 and R25. For full common mode testing, R22 through R25 needs to be selected to be 375 Ω as this is the standard for RS-485 devices.
| Associated Jumper | Signal | `Pad ID | Comment |
|---|---|---|
|
J7 and J6 | VCM_A |
R22 |
Common Mode Resistor Pad, 0603, to “A” |
|
J8 and J6 | VCM_B |
R23 |
Common Mode Resistor Pad, 0603, to “B” |
|
J9, J10, J11 | A and B |
C9 |
Termination Capacitor Pad, 0805 |
|
J9, J10, J11 | A and B |
R16 |
Termination Resistor Pad, 0805 |
|
J17 and J15 | VCM_Z |
R24 |
Common Mode Resistor Pad, 0603, to “Z” |
|
J16 and J15 | VCM_Y |
R25 |
Common Mode Resistor Pad, 0603, to “Y” |
|
J12, J13, J14 | Y and Z |
R19 |
Termination Capacitor Pad, 0805 |
|
J12, J13, J14 | Y and Z |
C10 |
Termination Resistor Pad, 0805 |