Noise on power/ground lines.....

Design Concepts
1

For all the embedded/uC people out there, I need some help.

I’m building a synthesizer project using an HC11 uC, and I’m running into a problem. My 74ls373 latch is very sensitive to noise. It latches spurious data if I’m not very very careful with where I hook it up. I’m just developing on a basic breadboard for the time being, but I need some help.

My breadboard looks basically like this: http://ece.bd.psu.edu/~cenbd451/lab/pics/P1061675.JPG

The only way I can get the latch to work right is to use a high quality motorolla latch, or by connecting my ground/vcc lines directly to the power supply entry point. I’ve got caps here and there between my ground/hot lines…but it doesn’t seem to help.

Can anyone help me out here? Thanks!

-Flecko

2

I have posted somewhere on this forum details of how I have reduced the noise inside my midibox significantly, though I can’t remember where. Maybe do a forum search on starlike or jitter or filter or something.

3

Ok, thanks. I’ll work out a bigger wire guage and some other ideas tomorrow. Thanks for the tips

-Flecko

EDIT: hehe, thanks

4

Heya Flecko!

.1MFD filter/bypass caps as close to the chip(s) as possible.  This works best when you use a filter capacitor on every IC.

Have you tried using pull-up resistors on the input/output/latch of the 373?

Just some random thoughts.    ;)

Have fun!

SmashTV

5

Hi Flecko,

how do you control the latch? Did you ensure that there is no so called “race condition” (e.g. data and clock at the same time)

Best Regards, Thorsten.

6

I’m using a PAL that triggers the latch on address match using the E clock and R/W signals from the HC11. The PAL i have controls all external glue logic for the HC11, so its working fine.

I ended up getting the latches stable by using a few different methods to reduce the noise, and it seems to be latching fine now.

Now I’m moving on to my CS problem…I’ll figure it out. Thanks for all the help Thorsten.

-Flecko