From: Jim Brain (brain_at_jbrain.com)
Date: 2007-04-10 20:05:57
Daniel O'Shea wrote: > Yes, I'm starting to think that a microcontroller might be the best > solution after all... what I'm trying to come up with is a > multi-purpose 9-pin controller that I can use to interface with an > XScale PXA270 processor, but also maintain C64 compatibility as an > alternate function. What's complicating things is that the C64 > joystick port has all its switches on the GND (0V) line, but the > PXA270 direct-keypad interface wants its switches on a 3.3V line... > Which at first doesn't seem like such a problem, until you want to > start adding in variable voltage sources that want a connection to > ground and power, if the ground and power lines are moving around! So > now what I'm thinking is if I input seven switches and two variable > voltages to a microcontroller, and then have seven outputs from the > microcontroller, with a jumper or toggle switch connected to select > between 0V and 3.3V mode, so then in 3.3V mode the seven outputs would > be: > > Up, Down, Left, Right, 3 buttons @ 3.3V (and X/Y variable voltage > sources which can bypass the microcontroller and be separately fed > directly to the PXA270, as it has its own ADC) > > ...and in 0V mode, the seven outputs would be: > > Up, Down, Left, Right, 1 button @ 0V and X/Y PWM outputs (here the > variable voltage sources are translated through the microcontroller's > ADC into PWM outputs for the C64) > > After a quick search I'm thinking a PIC16F87xA variant as it has > 10-bit ADC inputs, and two 10-bit PWM outputs - does this seem > achievable? (is the microcontroller's TTL I/O 3.3V?) thanks! I'll vote for the AVR. My PWM code is in C, which is easy to maintain, and you're free to it. The L (low power) AVRs can do 3.3v, and the outputs will track Vcc. 3.3v operation will yield 3.3v outputs. For the PWM code to work, you need 2 outputs for the POT lines, plus 1 IRQ (can;t be on of the outputs) 3 pins 5 JOY buttons = 5 pins 1 select jumper = 1 pin 9 I/O. Assuming one off DIP parts only, the ATTiny has 14 pin DIPs that offer what you need for $1.80-$2.50. If space isn't a premium, I vote for the ATMEGA8, a 28 pin IC that has plenty of program space and IO for what you plan to do. It's $3.66 in singles. You can add some more goodies to the code later, if you wish. PICs are a bit cheaper, though the programmers seem a bit pricier (I bought the PICkit 2 from Microchip for $35.00 or so, but my AVR programmer was free). Unless someone can spot you a HiTech PIC C compiler, you're into ASM for the PIC. If ML is a preferred language for you, then your original uC choice would be fine. I suggest C and the AVRs because I personally have moved beyond ML (I can do it, but I never could code it well, and free time grows shorter with each child's birthday). You may be in the same position (or a similar one). I suspect most of us are in that boat, as work and family encroach on the free time. Jim -- Jim Brain, Brain Innovations (X) firstname.lastname@example.org Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times! Home: http://www.jbrain.com Message was sent through the cbm-hackers mailing list
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