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Most any of the Mega chips would probably work. The Tiny stuff won't likely have enough pins so you could probably skip it. I've been working with the Mega128 recently on a project and find it to be fast enough with plenty of memory for my needs. And I am driving an LCD with it that has the HD44780 controller chip using just the half addressing (to keep pin count down) while also reading a serial data stream at 250 kbps and pulse-width-modulating an output at a 10 us duty-cycle. All while clocking the chip at just 16Mhz. (It goes to 20Mhz)

You will need a programmer and Atmel Studio 6. The software is available on their web site for free. You can save some money by purchasing the STK500 programmer (which will program the Mega128) or you can find a third-party programmer that implements ISP (In System Programming). And buy a few chips... they are cheap and you'll likely lock yourself out of at-least one. Everybody does at some time or another. Wink | ;-)

I think that you could probably have good success with this chip. You would need to identify the pins on the LC7981 that are connected to the microcontroller and figure out which is which. The good thing is that the LC7981 will only be connected to two things; the microprocessor and the LCD, so figuring out what is what should be pretty easy with the manual for that chip.

You *should* be able to set the pins on the AVR to high-impedence input mode and be able to pick-off the signals in-circuit... at least while you are testing and debugging. For a permanent install I would suggest desoldering the LC7981 and wire-up the pins on the Mega128 in its place. This is where a logic analyzer will be a big help. You'll need an acquisition rate at least twice the clock rate of the CPU in the device (likely 8Mhz but you may have to decode the information on a crystal to know for sure.) The analyzer will let you see the electrical signals as they happen in-circuit. The manual for the LC7981 chip should address the timing sequences for the pins which you should be able to verify with a logic analyzer. The manual will also talk about the initialization sequence and what, specifically, the chip will do for the different command modes. All this has to be provided so the guys writing the software on the micro side know how to drive the controller chip properly. The LCD controllers don't take serial commands... it is all at the bit level and driven by the clock... very low-level. But the manual for the LC7981 will cover all of that. Your task would be to write code for a Mega that would emulate this behavior. If I were attacking this I would likely figure out a way to execute an ISR (interrupt service routine) on the CS line. When the Mega sees this go high or low (depending on which is the 'valid' state), then the Mega can read/decode the data lines. Making it interrupt driven would be the way to go in my opinion.

There are some libraries out there for the Mega's that will drive various LCD controller chips. Looking at some of them might help you understand that side of the equation. You might also read up on http://avrfreaks.net and post some questions there. Note that the people there don't suffer poorly asked questions very well. You should make sure you have a well thought out and to the point question before you post over there.

There are also a lot of tutorials on sending serial data from an AVR chip to a PC. You will need that to send the data from the Mega to the PC. If I were you, I would probably try to keep this simple. Assuming the LC7981 works like most other controllers, the micro will load a character at a time onto the interface and clock it into the display controller. There are also control codes to clear the display, move the cursor, etc. I would turn those into similar control characters that could be send over the serial link while passing alpha characters as-is. If you do it this way, you could 'debug' the PC side of things using just hyperterm or something like that to read the stream of characters coming in. If the letters, numbers, and control characters are transmitted to the PC as they arrive at the AVR, you can pretty it all up in an app later.

You might also check and see if you have a hacker-space in your area. You can probably find someone there like me that knows the AVR stuff and might want to take this on as a project with you. This is the kind of novel project that guys like me are always looking for to take on as a personal project... out of the mainstream and yet very intriguing. I think the idea is cool and I could actually see something like this being useful beyond your project.
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