[sdiy] I/O trouble...

[Bert Schiettecatte]

Hi All,
 
On my daily adventures with microcontrollers I am faced with another I/O
problem. Please forgive me my silly questions since I'm not an
electronics expert. 
 
Here goes:
 
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). 
 
Thanks for any suggestions.
 
Bert (very tired and going to bed now)
 
 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20030711/006e6aef/attachment.htm>