262k-color qvga tft lcd screen pinout factory

You may have noticed that I have a bit of a ‘thing’ for the little TFT displays that you can commonly get on ebay. There’s something satisfying about writing your own driver code and seeing one of these little panels come alive with your graphics.

I hand-routed the traces and designed it so that the FPC cable from the 24-pin connector would wrap-around the board so that the LCD could be mounted on the opposite side to the LED driver components, with the 2.54mm MCU interface pins sticking up next to it.

Whatever you do, do not connect this circuit directly to a device with 5V levels such as the Arduino. The inputs and voltages are not 5V tolerant. An Arduino could be used to interface with this LCD with the addition of a level converter.

So far so good. No reason to get too excited though, in the above photograph all that I’ve done is test that the backlight circuit works and that the LCD powers up. Clearly it’s working so far.

You can also see four white LEDs wired in series in a breadboard behind the LCD. I used this LED string to test the output of the constant current driver before actually connecting the LCD. That’s why my development board exposes the V+ and V- output and feedback pins from the LED driver.

With the LCD mated snugly to the development board using double-sided sticky pads that keep it clear of the traces on the back of the PCB we’re ready to start reverse engineering the bus protocol.

Right away we’re on to something. Trawling through my collection of datasheets for TFTs I can see that the Leadis LDS285 uses 04h as its read device identifier (RDDID) code. The first byte returned by these controllers is always a dummy read, the real data is the values 54h and 80h, with 54h being the manufacturer code.

A quick search of the online list of MIPI manufacturer ids shows that 54h belongs to Arasan Chip Systems, Inc. Arasan is not a familiar name to me but their website reveals that they are engaged in making vertically integrated MIPI chipsets, i.e. the LCD controller, camera, file system etc. that you’d need if you were building a phone. The worrying news is that Leadis, whom we suspect of being the controller manufacturer have gone bust. I’m guessing that there is some kind of licensing agreement going on whereby Arasan and Leadis have collaborated to create an integrated controller.

Some random googling shows that there is someone else who’s experimented with LCDs from similar models to this one and determined that they tend to be command-compatible with a controller called the Magnachip MC2PA8201. This controller is itself a cut-down version of the LDS285. I’m going to assume that this is the one and see how far I get. Now it’s time to write an stm32plus driver for it and see if we can it to work!

The controller is documented to support colour depths up to 24-bit but this LCD will not go higher than 262K colours. Attempts to use 24-bit mode results in display corruption. This is not surprising given that the phone specifications are for a 262K colour display. Colours transferred in 262K mode must have their lower 2-bits zeroed.

Either some of the colours are verboten or this cheap LCD has problems with a very small subset of colours. Very rarely an attempt to write a run of a certain solid colour will result in weird corruption. This is odd because adjusting the colour by only 1-bit will correct the problem.

stm32plus 1.1.2 comes with drivers for the 64K and 262K colour modes for this LCD. You can see my usual demo sequence that exercises the capabilities of both the LCD and my graphics library in the video below.

The key to getting any of these TFT devices up and running is the initialisation sequence, i.e. what you have to do after power-on in order to get the display powered up and ready for commands. To help you on the way, this is the basic sequence for this controller. The extract is from the stm32plus driver, but the code should be self-explanatory.

In two of my previous articles I showed you how to reverse engineer the Nokia 2730 LCD for connecting to a device with 3.3V I/O’s and then I showed you how to build a 16-channel level converter for connecting devices together that have differing I/O level requirements.

This article brings together the knowledge we have gained in the previous two articles and puts it to use by creating a project that will allow a Nokia QVGA 24-bit colour TFT LCD to be indirectly connected to an Arduino Mega via a level converter, all on one small 50mm PCB.

All quite straightforward so far. The real innovation will be in the graphics library that I present in part two of this article set. The graphics library will use the external memory interface built in to the Arduino Mega to transfer data to the LCD in a single assembly instruction.

Perhaps the first surprise of this article is my choice of LCD. Given that the previous article showed how to reverse engineer the Nokia 2730 LCD you could have been forgiven for assuming that this was the one I’d use.

Well, since that project I noticed that a great many of Nokia’s QVGA displays seem to vary only slightly in their pinouts and as such the likelihood of them using the same controller would be high. I picked the Nokia 6300 for this project for the following reasons:

Here’s a photograph of the LCD side of the connector. If you look closely you can see where the ground pins connect directly into the ‘ground pour’ inside the ribbon cable. This helps to identify where pin 1 is located because the big “1” silkscreen’d on to the FPC is in the wrong place.

We need both 5V and 3.3V inputs for this design. 5V will be used to power the backlight driver as well as set the reference level for the Arduino side of the level converter. 3.3V will be used to set the reference for the LCD side of the regulator.

TFTs like these draw a very small amount of current, typically less than 10mA so I will supply it indirectly from a GPIO pin through the level converter. This allows me to control the order in which power is applied. Many TFTs prefer their I/O supply to come up before the panel supply and for safety I’m going to assume that this is the case with this device. Had the device required significant amounts of current I would have had to use a couple of transistors to switch the current on and off.

The Nokia 6300, like the Nokia 2730, uses an 8-bit 8080 protocol to communicate with the LCD. The 8080 protocol consists of a chip select signal, 8 bits of data, read and write lines and another line that is used to indicate whether you want to transfer data or set a command register value.

Selecting a low address line (A8) means that we can free up address lines 10 to 15 for GPIO, saving 6 pins. It doesn’t matter that our selected address locations 0x8000 and 0x8100 are high up in the address range who’s address lines are free’d for GPIO. The ATMega will still correctly control A8. Not only is this design fast, it’s frugal with pins too. Here is the mapping of Arduino pins to their LCD function.

Now that we have a design we can create the schematic in the Eagle designer. All the 5V signals from the Arduino that are destined for the LCD are routed through the level converter and will come out the other side at 3.3V.

After creating the schematic the next stage is to switch to the CAD designer and lay out the board. I placed the components and routed the traces manually. The connector is placed so that the FPC will wrap around the board edge and allow me to mount the LCD on the other side using double-sided sticky tabs.

With the LCD facing up, the interface pins face down and press directly into the sockets on the Arduino. The pin header is placed as close to the edge of the board as possible so that adjacent Arduino pins are not obscured.

After staring at the layout until I’m square-eyed (sound familiar to anyone?) I’m feeling confident that the header pins are all where they should be, the connector positioning will result in the LCD ending up in the right place and the silk-screening will end up on the correct side of the board.

I construct the boards by tinning the pads and then reflowing the larger components such as the level converter, LCD connector socket and the NCP5007 using a hot-plate. I then reflow the smaller discrete components using my Aoyue hot-air gun.

After the completed PCB is cleaned and dried the design is completed by pressing the LCD connector into its socket and mounting the panel on double-sided sticky pads. That it fits comfortably on to the pads was a bit of a relief because the metal back of the panel must stand clear of the traces and particularly the vias on that side of the board.

Another controller variant has turned up and we’re going to call this one ‘Type C’. It’s showing up in both 6300 and N82 screens. It behaves the same as Type A screens except for the following differences:

A 2.4” TFT LCD module consists of a bright backlight (4 white LEDs) and a colourful 240X320 pixels display. It also features individual RGB pixel control giving a much better resolution than the black and white displays. A resistive touch screen comes pre-installed with the module as a bonus and hence you can easily detect your finger presses anywhere on the screen.

The TFT comes with an auto-reset circuit which gets active on every breakout. However, a user can reset the module using this pin also, in case setup is not resetting clean.

The TFT comes with an auto-reset circuit which gets active on every breakout. However, a user can reset the module using this pin also, in case setup is not resetting clean.

Resistive Touch Pins – Y+, X+, Y-, and X- are the 4 resistive touch pins which require analog pins to read and determine touch pins. Their overlay is fixed at the top of the module which makes them electrically separate from the TFT. They can be used is 8-bit as well as SPI mode.

The 2.4” TFT LCD module supports many modes. However, two of them are very popular among users – “SPI mode” and “8-bit mode”. The display contains pins on both sides required for a mode and a user can switch easily between them by simply rewiring the display. It should be noted that only one mode can be used at a time.

A 2.4” TFT module has a very flexible usage. It is compatible with all your DIY projects where you want to add a bright, colourful, and touchscreen enabled display.