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Forum : Digole Serial Display :

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2-Wire SPI does not work (Arduino Nano/220x176 TFT)


I have an Arduino Nano and the 220x176 Color TFT module (shows Version 3.1). 3-Wire SPI works with DemoSketch without any problems. But if I hard ground the SS pin und set pin to 255 nothing happens on the screen. If I manually disconnect and connect again the ss pin from ground in 2-Wire Config everything starts working but only until the next powercycle.

That's very bad because I already layered and ordered a pcb that is designed for 2 wire spi with this modul.

Could anybody help?

Cheers, Chris

RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

 This is normal because If you ground the SS pin, you should make sure the SPI is Synchronized by yourself, the module will not know which bit is beginning, so, that why it only work when recycle the power.

So, when the SPI is grounded, the SPI port just shift each bit, if 8 bit received, transfer it as a byte of data to internal, it will not know which bit is start bit. That why SS pin is important, this pin will tell the module when a byte of transfer beginning.

You should keep CLK pin low when power up, wait till all circuit initialized, then send data via SPI, make sure no logic noise on CLK pin, if any noise or wrong operating on CLK, the SPI port will mis-aligned on bit, and then all data received in moudle are wrong. 

RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

Ok I understand. Thank you for your answer although this makes me not happy ;-)


But how is that practically done? I think you can't do that with the Standard-Digole-Lib and an Arduino - 2 Wire is probably not possible as discribed.

Could someone explain the last post based on an Arduino und the DemoSketches?

If you one-time activate the SS in 2-Wire-Mode it is impossible to switch to Grafik mode e. g. Display a Picture. The DemoSketch in 2-Wire Mode runs, if manually SS-activated, just finde - but doesn't display the Images. Perhaps some features never would run in 2-Wire SPI mode?


Cheers, Chris

RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

 According to our test and reported from other user before, the 2 wire SPI mode worked well if your follow the initiation sequency when power up, your problem may be sending data too much and drive the receiving buffer overflowed, so, try to add some delay (eg. 100ms) after each 1K data sent and reduce this delay until the module lost data.

RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

I tryed that before  - added up to 500ms delay before/between the commands.

But you sure that it worked? Actual test looks like this:

Breadboard with Arduino Nano, SS to GND, Data on Pin 8, Clock on 9 - Sketch: ColorGrafikLCDAdapterDemo (unmodified, or with delays - doesn't matter).  Init with 8,9,255.

Power UP: NOTHING, you have to release SS from Ground and reconnect at least one time - then the Display is "activated" - you can Reset the AVR and the Display remains working. BUT: The Images of the Demo Sketch are not shown.

With SS to Pin 10, Initiated with 8,9,10 - no problem at all. Images of the Demo Sketch show up.

My PCB ist high grade designed - no "Radio" or Garbadge on GND or any other Line - but as you see, the Breadboard-Test fails too. In one from 100 Power-Ups :-) , the Display starts working (without Images, see above) - but that is a bad hit-rate :)

I don't believe that it could run without any modifikation to Display FW or the Lib. I did some Tests with the CLK line but since the Arduino will power up, then LCD is initiiated, there is no possibility to LOW the CLK Line before the LCD init (doesn't make sense because the LCD init is the first real action you usually do in setup()). Another chance to not loose the PCB (was expensive to let produce) is softi2c but that the Lib must be rewritten und i2c is damn slow.

Cheers Chris


RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

 Try to add a pull down resistor between CLK and GND pins, or add a RC circuit on SS pin, this will avoid introduce any unwanted high logic level signal when your controller power up and the CLK is floating before initialized.

The SPI port in our moudle is hardware port, firmware will not able to fix the mis-aligned data. 

The image display well on the screen even SS not used according to our test.

RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

Looking at this Topic, maybe you could do better in firmware:


You could make the time when the spi initiates in the display configurable. "2.8 mode" and "3.1 mode" or something like that.

This would fix my problem also.


RE:2-Wire SPI does not work (Arduino Nano/220x176 TFT)

Here is the reset circuit we tested which work with Arduino Uno, the R2 will keep the CLK pin in low when host controller put this pin floating, R5 and C3 will keep SS pin disable in about 200ms when power up

You can change the R5C3 value to lower if your host controller initiated faster than Arduino Uno, and want the module receive the data and commands ASAP.

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