SPI interface with graphic LCD

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Electronics4you

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Hi there,

Has anyone tried to interface a 4-wire SPI interface graphical LCD? The display is of the +2.5-3.3 V type, so I use a voltage divider from my +5 V PIC18F4620 to lower the voltage on SCK and SDO. I initialize the display as shown in the datasheet https://www.electro-tech-online.com/custompdfs/2011/06/dogs102-6e.pdf on page 6, but the display doesn't react - no pixels light up. Chip select is always LOW and reset is HIGH.

Is there a fast test I can do to see, if the display is interfaced correctly with the PIC? I have used a scope to see the SDO/SCK signals, and they are find (charging/discharging curves of around 2.6-3.0 V when using a 3.0 V power supply).
 
hi,
Cannot help with the C, but what are the resistor divider values and is there a pull up resistor on the SPI lines.?

Edit.
**broken link removed**
 
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The resistors are 1k and 1k5, and no I have no pull up resistors on the lines. I'll just try that
 
Last edited:
Okay, figured out the PIC18F4620 can operate at 3V, so the voltage dividers are remove and pull up resistors have been used. Still there is no response from the display. Does the display require a special timing of the control signals?
 
Electronics4you said:
Okay, figured out the PIC18F4620 can operate at 3V, so the voltage dividers are remove and pull up resistors have been used. Still there is no response from the display. Does the display require a special timing of the control signals?
Click to expand...

hi,
Do you have this pdf.?
 

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Yes, I have tried to read it, but it does not seem different (timing wise) from the initialization example in the datasheet of the display. All commands are just transmitted to the display using the standard SPI module in the PIC. Thus, the timing of the SCK and SDO signals must be in order. Now I can see the datasheet shows non-polarized capacitors, but I used electrolyte capacitors - will that change anything? If mounted correctly there should be no problem, right?
 

It dosn't specify non polarised caps.?
Do you have any non polar caps to try.

Is the LCD showing any pixel blocks.? after you try to initialise it.??

Also have you initialised the Contrast .?
 

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Ia have initialized the contrast with the "Set contrast" SPI command, so I figured that would be on a default level. Also I see no pixels blocks at all, but I know the display is not defect. The non-polarized caps did not make a change at all. I think it is strange, since the hardware only requires simple VDD or VSS connections along with the SPI output from the PIC
 

hi,
I have looked thru the documentation for the LCD.
How do you have the CD[A0] and /CS0 pins connected.?

Also the Reset pin.?
 
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Electronics4you said:
CD = LOW (command)
/CS0 = LOW (chip always selected)
RST = HIGH (no necessity of resetting the lcd module during operation)
Click to expand...

hi,
Its normal to apply the system /reset pulse at power up.? as the d/s states
 

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