AW: [sdiy] I/O trouble...

[Ullrich Peter]

>I have a MCU with 2 8-bit ports available, one of them is the A/D. Since I'm
connecting an LCD to the MCU as well, I need one port as the LCD's data bus. 
>So that leaves me without any pins to light my LED matrix (32 leds = 4x8) and
scan my key matrix (up to 32 keys). 
> 
>I thought about putting an SN74CBT16233 on the 2 8-bit ports, this will give me
another 16 I/O lines. This IC is a 16-bit 1-of-2 FET multiplexer. So I would 
>put the A/D and LCD data bus on one output of the multiplexer and the key
matrix + led matrix on the other output of the multiplexer. The key and led
matrix 
>would be 8 rows which I want to put power on sequentially, and then use 4
columns to light the LEDs and 4 columns to scan the keys. Does this make 
>any sense? I'm just trying to find a way to hook up all this I/O. Argh! 
> 
>It's ok if I lose some brightness by multiplexing, as long as they have a
decent visibility I'm happy. I'm also concerned that the MCU might go to heaven
if I 
>make it source and sink the current for the LEDs (even when only one LED gets
lit at a time for a very short period). 
 
You could attach an 8279 keyboard/display controller to the microcontroller bus!

This controller can scan a keyboard with I think about 64 keys and can control 
8x8 LEDs. You get an interrupt when a key is pressed, too.

I used this part sometimes and it works fine!

datasheet is here: http://my.dreamwiz.com/pentam/databook/8279.pdf

But before using it check the availability!

Ciao
Peter

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