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DESCRIPTION

Have you gazed longingly at large TFT displays - you know what I'm talking about

here, 4", 5" or 7" TFTs with up to 800x480 pixels. Then you look at your Arduino.

You love your Arduino (you really do!) but there's no way it can control a display

like that, one that requires 60Hz refresh and 4 MHz pixel clocking. Heck, it doesn't

even have enough pins. I suppose you could move to ARM core processors with TTL

display drivers built in but you've already got all these shields working and anyways

you like small micros you've got.

What if I told you there was a driver chip that could fulfill those longings? A chip

that can control up 800x480 displays, and heck, a resistive touchscreen as well. All

you need to give up is 5 or so SPI pins. Would you even believe me? Well, sit down

because this product may shock you.

The RA8875 is a powerful TFT driver chip. It is a perfect match for any chip that

wants to draw on a big TFT screen but doesn't quite have the oomph (whether it be

hardware or speed). Inside is 768KB of RAM, so it can buffer the display (and

depending on the screen size also have double overlaying). The interface is SPI with

a very basic register read/write method of communication (no strange and

convoluted packets). The chip has a range of hardware-accelerated shapes such as

lines, rectangles, triangles, ellipses, built in and round-rects. There is also a built

in English/European font set (see the datasheet section 7-4-1 for the font table)

This makes it possible to draw fast even over SPI.

The RA8875 can also handle standard 4-wire resistive touchscreens over the same

SPI interface to save you pins. There's an IRQ pin that you can use to help manage

touch interrupts. The touchscreen handler isn't the most precise driver we've used,

so we broke out the X/Y pins so you can connect them up to something like the

STMPE610 which is a very classy touchscreen controller.

On the PCB we have the main chip, level shifting so you can use safely with 3-5V

logic. There is also a 3V regulator to provide clean power to the chip and the

display. For the backlight, we put a constant-current booster that can provide