P-P-PIC up a TFT with chipKIT and DisplayCore

Did you know that chipKIT boards are probably the best choice for controlling a TFT screen?… Considerably better than most Arduino boards, that is for sure! I say that with confidence for three reasons:

  1. chipKIT boards typically have far more memory and computing power than many Arduino boards, and as a result, they are so much better at manipulating graphics and data for display.
  2. chipKIT boards can get the data out to the TFT screen so much faster though high-speed interfaces, so less time is spent redrawing things on the screen. You’ll find that images appear instantly, as opposed to being drawn out slowly.
  3. Finally my favourite reason: professional-grade library support. I say it’s my favourite because I designed and wrote the library myself, but I’ll tell you more about that journey later on.

First let me introduce you to a little friend of mine:


This here is the Picadillo-35T developed by 4D Systems in Australia (also available from microchipDIRECT). The Picadillo is essentially a chipKIT MAX32 board with a nice, high-resolution TFT touch-screen strapped to the back. The meaty PIC32MX795F512L chip (also used on the MAX32) boasts plenty of RAM (128KB) and Flash (512KB) and all the other bells and whistles you have come to expect from chipKIT boards. The board also has the same connectors as the popular chipKIT Uno32, uC32, WF32 etc., so all your shields should just plug in and work. You also get sound thrown in to the mix with an on-board speaker, and of course you get an SD card slot–what self respecting board would be without one these days anyway?!

Ok, enough said about that. The main reason I write this post is to tell you of the most useful part of this Picadillo board: the TFT touch-screen. And let me tell you, it’s not just any TFT screen. It’s an above-average 3.5″, 320×480 resolution, crisp-image delivering screen. Not only that, but the way the TFT is wired to the PIC32 chip is also “above average.” The TFT connection boasts a 16-bit parallel interface, not the normal slow SPI interface that most cheap Arduino TFT screens give you–meaning that it takes one bus clock operation to output a pixel as opposed to 16 (a considerable speed increase!).

But that’s still not all! (I’m starting to sound like a TV salesman now. “Buy now and we’ll throw in this amazing clock radio and set of saucepans absolutely free!”). The TFT’s 16-bit interface has been directly connected to the “Parallel Master Port” (PMP) of the PIC32. The PMP is a bit like the old internal bus of early computers; you get an address bus, a data bus, and a bunch of control signals, meaning there’s no messy twiddling of GPIO pins with the likes of digitalWrite() (or even direct port manipulation using registers). Writing data to the screen takes just one instruction. That’s right – ONE instruction. And that means even greater speed. But wait, there’s more! (Here comes the gold-plated nose-hair trimmer…) It’s called DMA: Direct Memory Access. Guess what that can do! DMA can send data through PMP, and this essentially allows for direct communication with the TFT display, all without the MIPS CPU’s involvement! In effect, you can be outputting data to the screen whilst doing other things! All-in-all it’s really a thing of beauty… if you like that kind of thing, of course.

So what does all that mean to the layman? It means you have a well-designed, well-built bit of kit in a nice compact package with all the power you could ever want to make your perfect user interface. But isn’t programming user interfaces and drawing graphics on a TFT screen a hard job? Isn’t it fairly skilled and in-depth? Don’t you have to write reams and reams of code just to get it to print “Hello World”? Well, yes, you do. However I have already done all that for you. And that is where the journey to the core begins.

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