Detect if LCD connected

Vincent31

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Subject:

Detect if LCD connected

· Posted: 31.03.2021 - 17:01 · #1

Hello all,

I have a quick question...I am using a LCD display 2x16 on PortC, no problem, I import LCDport in program, but when LCD is not connected, my AVR has strange behaviour and becomes very slow...because I suppose all pins PortC for LCD are not connected...So is there a function to detect if LCD is connected or not, and if not disable LCD port and put it as simple output for example...like DDRC=$FF

Because my harware need to work with or without LCD....thanks for your help

Vincent

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Re: Detect if LCD connected

· Posted: 01.04.2021 - 11:28 · #2

Hello Vincent31 ,

how is your LCD connected? 4bit, 8bit, SPI or I2c bus?

Which CPU ATMEGA or XMEGA?

E.g. with the I2c with an XMEGA you could use TWIstatE () to query whether the display is even available.

With the SPI, if the display has a read option, just read and switch off at TimeOut. You can e.g. write in a register and then just try to read from it, if it is there, you will get the written back, if not you run into the TimeOut and switch it off.

Hardware Option:
Many displays often have several GND pins, here you could simply query an input of the CPU with a pull-up.

If it is high, then it has positive power via the pull-up, if it is low, then it is pulled to low via a GND pin from the connector of the display and a display is available.

Thorsten

Harry

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Re: Detect if LCD connected

· Posted: 01.04.2021 - 11:47 · #3

Hello Vincent,

I think you must not use the automatic initialisation of the display. First determine whether a display is connected, then initialise it manually. It doesn't matter which interface the display uses.

Harry

Vincent31

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Re: Detect if LCD connected

· Posted: 01.04.2021 - 13:00 · #4

Hello Harry and Thorsten,

Thanks for reply. I am using Xmega64A4U, on PortC so not SPI or I2C, also, hardware is finished, cannot add pull up on LCD connector...

Harry, may be you are rigth, could add in program the compiler switch {nolcdinit) and test portC if LCD connected manually, and if connected launch function LCDinit of driver...

Now I have to see how testing if LCD connected, may be with a time out ?

Vincent

Harry

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Re: Detect if LCD connected

· Posted: 01.04.2021 - 14:07 · #5

Hello Vincent,

you can only test one output of the LCD or input on the controller. Switch on the PullUp or PullDown (depending on the level) of the controller and see if the LCD works against it.

Harry

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Subject:

Re: Detect if LCD connected

· Posted: 01.04.2021 - 15:27 · #6

Quote by Harry

Yes, I think Harry's solution here is the simplest, with no hardware changes.

Thorsten

Vincent31

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Subject:

Re: Detect if LCD connected

· Posted: 01.04.2021 - 16:04 · #7

Thanks, yes I think good solution, but AVRco should have a driver function to test if LCD connected....

Vincent

Detect if LCD connected

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