[LCD3 Cape] Purpose of 33 ohm resistors on LCD buffer

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1

What is the purpose of the 33 Ohm resistors in series with all the LCD lines on the buffer for the LCD3 cape? Are they actually required or is it just ‘good practice’ to terminate the lines like that?

Schematic can be found here: https://github.com/CircuitCo/BeagleBone-LCD3-RevA2/blob/master/BeagleBone-LCD3-RevA2-schematic.pdf?raw=true

Thanks,
Max

2

Prevents reflections due to impedance mismatches. Reflections cause noise on the signals.

Gerald

3

Thanks for the quick response. Is the value of 33 ohms calculated/lookedup/choosen to match something specific or is it just a ‘typical’ value?

Thanks,
Max

4

It is typically between 22 and 33. In some cases the LCD suppliers show the value in their datasheets or application notes.

Gerald

5

Good to know. Thanks for the response.

Thanks,
Max