Finding the protocol used to communicate with a LCD  - Page 1
Forum section: electronics / projects

author: Irilia
author_rank: Regular Contributor
timestamp: December 19, 2024, 08:13:49 am
content: I can find out the data pin from the power pin, but otherwise I have no idea how to get more information, the reference of the LCD don't get anything back: 8S28023 WaterupⓇ2022.04I have a basic oscilloscope, multimeter and a generic USB 8 channel Logic analyzer (probably I need to use)The pictures are included

author: jpanhalt
author_rank: Super Contributor
timestamp: December 19, 2024, 11:15:55 am
content: Can you give a little more information? Is the LCD from a device or standalone? Monochrome or color? Character or graphical? If it's bare graphical monochrome LCD, there are 3 common interfaces (parallel, SPI, and I2C) and the pinouts are similar, but not identical, for each interface. See attached. A 20-pin connector/flat cable may be used even though not all 20 pins are used. The board you show is quite a bit more complex than a typical bare display, so it might be from some device/instrument.

author: squadchannel
author_rank: Frequent Contributor
timestamp: December 19, 2024, 11:24:20 am
content: from the 14-pin data and the board design, is not using a high-speed bus. probably SPI.do you know the resolution, screen size inches?

author: peter-h
author_rank: Super Contributor
timestamp: December 19, 2024, 03:48:05 pm
content: If it is a video application, it could be MIPIhttps://www.synopsys.com/blogs/chip-design/what-is-mobile-industry-processor-interface-protocol.htmlwhich is "out of luck"

author: Irilia
author_rank: Regular Contributor
timestamp: December 19, 2024, 04:29:41 pm
content: Hear are some more information >1 2 3 4 5 6 7 8 9 10Bl Vcc gnd 3.3 3.3 ? D? D? D? D?11 12 13 14 15 16 17 18 19 20? D? D? D? D? D? D? D? D? gndAnd other things in the picture

author: ajb
author_rank: Super Contributor
timestamp: December 19, 2024, 05:06:05 pm
content: Could be SPI, but also could be an 8-bit parallel interface. The 11x data lines with 10R series resistors makes me think the latter. A typical parallel interface would be 8 (or 16) data lines, clock, data/command select, and reset, which lines up with those 11 obvious connections well enough. There are 18 contacts used on the FPC, so that leaves one remaining signal, which could be a sync line to prevent tearing, an interface mode select line or something, or even unused.If you can trace those lines back to the MCU, you may be able to confirm the assignments by checking against the functions available on those pins. It's fairly common to use an MCU's parallel memory interface to drive parallel LCDs, but it could also be driven from a GPIO port. If it's using SPI, then of course you'd expect to see some of those connections land on an SPI interface.In any case, do you have a logic analyzer or multichannel oscilloscope you can use to probe the pins? If you can probe four or more of those signal lines at once it should be fairly easy to find out what's going on with the interface -- the patterns on the clock, d/c, reset, and data lines will be very distinct from each other. It's possible to do with a 2-channel scope as well, but will be harder to see the relative timing of the various signals. Figuring out the assignments of the individual data lines will be harder.Are you trying to reuse the display for another project, or trying to find a replacement?

author: jpanhalt
author_rank: Super Contributor
timestamp: December 19, 2024, 05:09:08 pm
content: I suspect from what you show that the board in your first post is the device to which the LCD is attached. THe drivers and hence protocol are covered by the white plastic case.The resolution appears great and blue and white suggests it is not monochrome.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 19, 2024, 05:29:34 pm
content: 11 lines might be 8 data + 3 control lines from the classic HD44780 interfacehttps://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller

author: Irilia
author_rank: Regular Contributor
timestamp: December 19, 2024, 05:29:53 pm
content: Quote from: ajb on December 19, 2024, 05:06:05 pmyes it was in my first message (I said the logic Analyzer was probably the best tool in what I have for that)No I want to recover the signal to control another Display, because for one this display is bad, and secondary the interface is way too gimmicky I just want a clear display of what happens.I could probably look at to the code inside the micro controller, but I suspect it will be not accessible and I will not understand anything anyway.

author: squadchannel
author_rank: Frequent Contributor
timestamp: December 19, 2024, 05:40:44 pm
content: OWON SPM3051?2.8inch color TFT320x240 ILI9341?

author: jpanhalt
author_rank: Super Contributor
timestamp: December 19, 2024, 06:06:50 pm
content: I saw that SPM3051 label and didn't associate with with an LCD. Good catch.Here's a link to its datasheet:https://www.digikey.com/htmldatasheets/production/1640716/0/0/1/ili9341-datasheet.htmlThe logic analyzer should resolve the protocols (SPI is only 1 or 2 data and others are control lines).

author: Irilia
author_rank: Regular Contributor
timestamp: December 20, 2024, 01:20:37 am
content: Thanks for the help I have to look at that 😊

author: squadchannel
author_rank: Frequent Contributor
timestamp: December 20, 2024, 01:32:50 am
content: I gave ILI9341, which is often used as an example, but ST7xxx, and there are still many others.Sniff the SPI would be a good idea.

author: amyk
author_rank: Super Contributor
timestamp: December 20, 2024, 03:41:08 am
content: Definitely a parallel interface LCD with its own framebuffer.ILI9341 is a "wide Philips" command set (the 2A/2B/2C commands are inspired by the old PCF8833); the other common one is "wide Epson" that uses 15/75/5C instead, and there's a somewhat less common Samsung one with 42/43 commands as well as miscellaneous others.Reference:https://web.archive.org/web/20120123023608/http://wiki.s1mp3.org/LCMControllers

author: Irilia
author_rank: Regular Contributor
timestamp: December 20, 2024, 03:55:38 am
content: Ok you strat to lose me here, do I connect the logic Analyzer directly to the pins before or after the resistor, do I need to add a resistor before the analyzer ?

author: amyk
author_rank: Super Contributor
timestamp: December 22, 2024, 06:02:30 am
content: Shouldn't matter; your LA inputs should be high enough impedance to not affect the functioning of the circuit.

author: Irilia
author_rank: Regular Contributor
timestamp: December 22, 2024, 07:30:42 am
content: Ok thanks 👍