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Topic: What’s the difference between these two ST7920 lcd’s? (Read 5142 times) previous topic - next topic

satoer

I'm trying to recreate I project I've done for a friend. In this project I used an atmega1284p and an ST7920 lcd with SPI. I thought I ordered the same parts, and although the pinout description is the same, the PCB's are different.


My project was done with LCD B, and hooked up like the attached schematic.


Using Hardware SPI on a atmega1284p, LCD B and u8glib. This worked fine.

But now I've recreated the project the same way, but now with LCD A. This gave me a short-circuit. After investigating it turned out the resistance between pin PSB (marked CS1 in the schematic) and pin Vdd on LCD A is 0,7 Ohm. In display B te resistance is 10 mega Ohm. With LCD A this gave me the short-circuit.

Anyhow. Can anyone tell me the difference between these display's and why LCD A refuses to work?

satoer

 :-[  :-[ This is so stupid... Took me the whole day investigating and 15 minutes after posting this topic I have found the answer.
 
Turns out LCD A is hard wired into parallel mode. To enable SPI you have to remove R9 on the PCB. Now it works fine :)

Maybe someone else has the same problem and find's this solution otherwise sorry for the wasted server space. ;)

mainlin

Someone will eventually have the same problem and hopefully, they find your post.

mnbv

Dear satoer

Hi!

I have a similar (but not same) problem!

I am using atmega32a + LCD B with parallel mode (psb --> vcc)

My project is running on proteus but not in real circuit!

Can you help?  :|

raphaelfribeiro

Someone got simulate the ST7920 in Proteus? I'm using Proteus 8.5 version.

I want to buy this: http://www.filipeflop.com/pd-6b7ea-display-lcd-grafico-128x64.html

gsvincze

I'm trying to recreate I project I've done for a friend. In this project I used an atmega1284p and an ST7920 lcd with SPI. I thought I ordered the same parts, and although the pinout description is the same, the PCB's are different.


My project was done with LCD B, and hooked up like the attached schematic.


Using Hardware SPI on a atmega1284p, LCD B and u8glib. This worked fine.

But now I've recreated the project the same way, but now with LCD A. This gave me a short-circuit. After investigating it turned out the resistance between pin PSB (marked CS1 in the schematic) and pin Vdd on LCD A is 0,7 Ohm. In display B te resistance is 10 mega Ohm. With LCD A this gave me the short-circuit.

Anyhow. Can anyone tell me the difference between these display's and why LCD A refuses to work?

If you still looking for a solution I think it's might help.

You need to remove the two 0 Ohm resistor named R9 and R11, read it somewhere a couple years ago when I used this display. I know this because mine is a "version A" and those two are not on the board and I remember removing it. I think it's the selection of SPI or parallel input.

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