LCD poroblem


New member
In my design, the LCD controller is inside the MCU, (i.e. no interface available). So, I can't use SPI or I2C to get the commands that are going to the LCD.

can I do it with MCU segment pins directly (I have 40 segment pins and 4 COM pins , Total: 40x4=160 segment but I am worried about voltage level it’s not 3.3v or 0v )

What’s your experience?
what are your suggestions?

Thank you.
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New member
sorry for not being clear enough . .

usually the MCU (Micro-controller Unit) is connected to the LCD via an LCD controller, and the LCD controller is connected to the LCD via the 40 segment pins and 4 COM ports. This way, a SPI or I2C bus can be used to test the commands that are going from the MCU to the LCD controller.

However in my case, I have a Micro-controller Unit (MCU) that has the LCD controller integrated in it.

My question is: how can I know know the commands now where there is no bus to spy on? can I know the commands from the 44 pins? Is there any suggestions on how I test the commands?

In my design, ...
This implies several things.

First, that you have control over the choice of hardware, and you have chosen a method that does not allow access to the LCD commands, which you want, presumably, for troubleshooting purposes.

Second, that you have control over the firmware, so that you already know what commands are being send to the LCD.

One can assume that the MCU has more I/O than just the LCD panel segments and backplanes. If the MCU part number is not a secret, maybe you could reveal it, and make it easier to understand what your situation is.

You can't use the LCD output pins to monitor anything. But, it should be a simple matter to add code to your firmware that sends a SPI-like serial stream from an unused output pin, so that you have a way to monitor the commands. You could also use an input pin to control your program flow, to make it easier to troubleshoot. I am assuming that your MCU does not have a single-step or debugging method already provided by your development tools.