5 years, 8 months ago.

RE: 4x8 segment LCD on KL-46Z comX pins

How do I find out if the com0-3 pins are common anode or cathode ?

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The FRDM-KL46Z is an ultra-low-cost development platform enabled by the Kinetis L series KL4x MCU family built on the ARM® Cortex™-M0+ processor. Features include easy access to MCU I/O, battery-ready, ...
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2 Answers

5 years, 8 months ago.

From the schematic/module number? But do you mean the integrated LCD? This library exists for it already: https://mbed.org/users/Sissors/code/SLCD/

Yes, I am referring to the 4x8 segment LCD that comes with the KL-46Z board. I will try to use the SLCD library. Many thanks.

UPDATE: I tried your SLCD library and it works beautifully. Thanks again.

posted by samira samilan 25 Mar 2014
5 years, 8 months ago.

LCDs should not be driven with DC voltages. The terms common cathode/common anode make no sense in this context. The common electrodes are used to multiplex the segment pins but they will have a waveform that reverses polarity for every other frame. This is needed to prevent damage to the LCD. Dont try to drive an LCD directly from the processor pins unless you understand how it needs to be done.

Thanks for the explanation. Question: I have done 4 digit seven segment before with AVR/arduino.

Are you saying that the built in 4 digit LCD that comes with KL-46 is different from the regular 7 segment LED ? So, I can not use the multiplexing method/ Persistent of Vision(POV) technique ie. turn on/off each digit very fast ? I am awaiting your answer before I will try it. Thanks again for your prompt response. I REALLY appreciate Erik Olieman and your helps. It has helped me a lot.

posted by samira samilan 25 Mar 2014

A regular 7-segment LED is as it already says, just 7 LEDs in parallel. The LCD display of the KL46Z is an LCD display, and are not just straight forward LEDs. They require different control, there is also for example a charge pump to make the required voltages.

But at the same time it consumed only very little power. The multiplexing method still works, but it is not as straight forward as for 7-segment LEDs. The display is connected to a specific peripheral of the KL46Z which can generate the required signals, and the SLCD library controls that peripheral so you don't need to worry about anything. (It is example code from Freescale modified for mbed).

posted by Erik Olieman 25 Mar 2014