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'[PIC] NVRAM and PIC'
2006\04\01@102854 by PIC

picon face
Hi,



Recently, I've started using NVRAM - Dallas DS1225AD - 150 in my design.


I designed a little "interface board", on which I put my NVRAM. It
connects it with ribbon cable to my PIC board ( also designed by me ).

I write something to RAM and then I read it several times. Every time I
read it I get some of the data different than it was when I read it the
previous time.

I thought that it could be something with timing so I extended reading
times. I made much longer than the minimum values in datasheet. It
didn't help.

I read in datasheet that the input have to be stable for certain time to
get data from it. The only possible cause coming to my head is that
outputs from my PIC board are not stable.

Could it be the cause of it?

Is there any possibility of checking stability of outputs on PIC without
using oscilloscope?

What could cause unstable outputs on PIC?



I'm using PIC18F8621 running at 40 MHz. Programming in Microchip C18.



I would be very grateful for help.



Thank you and best regards,

Sam



 

2006\04\01@170016 by Jinx

face picon face
> on which I put my NVRAM. It connects it with ribbon cable
> to my PIC board ( also designed by me )

How long is the ribbon cable ? I had something similar ages ago
and found that having pull-downs on the data lines helped. They
were 100k I think, in an array with a common

2006\04\02@132144 by Sam

picon face
I made the cable half of that it was and it appears that it helped. :-).
It was half meter long.
I wouldn't expect that length of cable could have such influence on my
design.

Thank you very much,
Sam

-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf
Of Jinx
Sent: 01 April 2006 23:00
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] NVRAM and PIC

> on which I put my NVRAM. It connects it with ribbon cable
> to my PIC board ( also designed by me )

How long is the ribbon cable ? I had something similar ages ago
and found that having pull-downs on the data lines helped. They
were 100k I think, in an array with a common

2006\04\02@182312 by Jinx

face picon face
> I made the cable half of that it was and it appears that it helped. :-).
> It was half meter long.
> I wouldn't expect that length of cable could have such influence on my
> design.
>
> Thank you very much,

You're welcome

I'm no expert on digital noise, but I do know the length of eg ribbon
cable can deteriorate signal quality through crosstalk, impedance mis-
matching, reflections and propagation delay. IME, over about 30cm
starts causing problems with micros

Not sure what you'd Google for to get the best example and remedy

http://www.sigcon.com/Pubs/news/3_10.htm

2006\04\05@000841 by kravnus wolf

picon face
the length cause capacitance issues. read it up. very
important to know the lengthy problem :D

john

--- Sam <picspamKILLspamamusementcity.com> wrote:

> I made the cable half of that it was and it appears
> that it helped. :-).
> It was half meter long.
> I wouldn't expect that length of cable could have
> such influence on my
> design.
>
> Thank you very much,
> Sam
>
> {Original Message removed}

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