[sdiy] mcu project with too few I/O lines :(

[Leif]

since you are using atmel mcu's... they support i2c/twi... look at philips 
PCA9555 (16 bit i/o with interrupt) and PCA9552 (16 bit led driver). you 
can have 8 of each of them on the same i2c/twi line... so that gives you 
128 i/o's and 128 possible leds... there are also PCA9554 with an external 
reset instead of an interrupt. and there is a SAA1064 led driver. also ok 
to use.

Also you can add a i2c bus expander and run several i2c buses with 
different addressing... for instance one 8 bus expander gives you 8 i2c 
buses run on one... you can then have 1024 i/o's... If you then use 
interrupt chips (also availble from philips) for using interrupt vectors 
you can then have interrupts from all the chips and always know which chip 
got an input... for outputs the interrupts can also trigger if you program 
them to.

Cheers,
Leif

At 20:23 23.05.2003 +0200, Bert Schiettecatte wrote:
>hi all,
>
>i'm doing a microcontroller project here with an optrex graphical
>display (128x64), rotary encoder, led matrix (16 leds), and key
>matrix (16 keys). of course there is also the midi and in system
>programming connectors. unfortunately my microcontroller (atmega8)
>does not have a lot of i/o lines available, and I'm left clueless
>how to interface all that stuff to it. The display has an 8bit
>data bus + a few i/o lines for reading, writing, etc. for the
>led matrix, i'd like brightness control for each led (PWM?).
>
>I thought about using a key encoder and maybe an LED driver but
>those ICs are pretty expensive (7$ for a key encoder, that's more
>than a microcontroller!). does anyone have some advice here and
>how to interface this stuff without buying tons of additional ICs
>which cost a lot of $$$?
>
>thanks,
>bert