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You can see a LCD wired on a board above. based on the back of its board, it has 8 pin and its seventh pin and eighth pin is connected to VCC and GND. I search in internet for datasheet of this LCD. But I found nothing. Does any one know where I can find it? What kind of protocol does it use to communicate with MCUs?

And how I can monitor its pin to see the data transfers between it and a MCU? (I don't have scope or logic analyser. I want to monitor its pins by an Atmega32 and send the data to my computer's COM port. but I don't have any idea how!)

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  • \$\begingroup\$ It's pretty hard to make much out of things, but how does the 14 pin LCD end up connected to the eight pins? 14 pins is pretty common for an LCD without a backlight and there's a few fairly common pin configurations. \$\endgroup\$ – PeterJ Dec 16 '14 at 10:10
  • \$\begingroup\$ @PeterJ Maybe it use serial communication for data command! for example one pin for data/command - one pin for EN- one pin for RS -one pin for .... I don't have any idea! :D I want to find the answer! \$\endgroup\$ – TheGoodUser Dec 16 '14 at 10:11
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    \$\begingroup\$ For the protocol, I'm guessing I2C? Do you have a serial number somewhere? @PeterJ I think the 14 pins are one half of the uC. \$\endgroup\$ – Keelan Dec 16 '14 at 10:14
  • \$\begingroup\$ @CamilStaps I think so also. No I can't, The LCD wired on the PCB and I can't see anything except than the screen. \$\endgroup\$ – TheGoodUser Dec 16 '14 at 10:27
  • \$\begingroup\$ You could desolder it, no? The connector is not too small, you can put it back after. \$\endgroup\$ – Keelan Dec 16 '14 at 10:31
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I called the manufacturer and they answered me :

From left to right :

DB7 | DB6 | DB5 | DB4 | En(Clock) | RS | VDD | VFF

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    \$\begingroup\$ If that answers your question, accept it. \$\endgroup\$ – Wouter van Ooijen Dec 16 '14 at 13:02
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    \$\begingroup\$ In the future, it would be better to try calling them before asking the question. This question will be rarely useful for future visitors. \$\endgroup\$ – Keelan Dec 16 '14 at 13:13
  • \$\begingroup\$ @WoutervanOoijen elelctronics.stackexchange.com makes me wait 24 hour to accept my answer as the correct answer! \$\endgroup\$ – TheGoodUser Dec 16 '14 at 13:47
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    \$\begingroup\$ Standard HD44780 LCD type interface operating in nibble mode. Saves four pins over the standard LCD interface that has all of DB7 -> DB0 pinned out. \$\endgroup\$ – Michael Karas Dec 16 '14 at 15:15
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There are too many options for a 2x8 8-pins LCD. You will have to desolder it to see if there's a serial number or something.

As for the interface: as far as I know I2C is the most popular serial protocol for character LCDs.

I didn't expect a parallel interface as the most common one (HD44780) would need more than 8 pins. It normally has 11 lines (8 data, 3 for R/W, RS and E). In nibble mode it just uses 4 data lines, making the whole interface 7 pins. With the power pins and a pin for contrast that gives a total of 10 pins, 2 too much.

Looking at the other answer however, they made a HD44780-like interface, leaving out the RW (so you can't read from the display) and the contrast (so you can't handle the contrast yourself, or there's a trimmer on the board), which gives 8 pins.

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  • \$\begingroup\$ I2C is not the most common interface for character LCD modules. The most common is the standard 8-bit HD44780 interface. Second most common is the HD44780 operating in nibble mode so four less pins are required. Some controller chips these days do have intrinsic support for either I2C or SPI type interface that can be selected via strapping pins but these are less common. There is an after market for I2C adapters that allow running a standard HD44780 interface in nibble mode from an I2C port. They can be found on eBay and like sites for a low cost. (continued) \$\endgroup\$ – Michael Karas Dec 16 '14 at 15:24
  • \$\begingroup\$ (continued from above) Many of them can solder right into a standard LCD module set of interface holes to direct convert the module to I2C. \$\endgroup\$ – Michael Karas Dec 16 '14 at 15:24
  • \$\begingroup\$ @MichaelKaras you are right, but I was talking about serial protocols, and the HD44780 interface uses a parallel protocol. An HD44780 in nibble mode still needs the RS, RW and E signals, so it needs 7 data lines, with the power pins, is a minimum of 10 (or maybe 9, if the contrast is on-board) pins. Hang on, I now see the other answer, the RW pin is left out, that allows 8 pins indeed. I adapted my answer to clarify, thanks. \$\endgroup\$ – Keelan Dec 16 '14 at 15:26

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