gnupic: PIC driving an 24LC256...
Subject:
PIC driving an 24LC256...
From:
####@####.#### (Rogier Wolff)
Date:
19 Sep 2001 21:37:35 -0000
Message-Id: <200109192137.XAA00395@cave.bitwizard.nl>
Hi Guys,
I was wondering if one of you could drop a quick look at my project.
I'm trying to drive an 24LC256 (256kbit eeprom) from a PIC 16F873 .
The problem is that when I try to read back the data from the eeprom,
it seems as if the eeprom is WAY late in starting to drive the data
line.
To write to the eeprom:
S 1 0 1 0 0 0 0 0 A 0 0 0 1 0 0 1 0 A 0 0 1 1 0 1 0 0 A 1 1 1 1 1 1 0 0 A S
T C C C C T
A K K K K O
R P
T A 0 1 2 3 4 F C
I get "acks" at the right time, and so forth. All seems well.
However, when I try to read from this same location, I see the
EEPROM take control of the data line WAY too late.
We've tied a weak "pull-to-the-middle" on the data line so that we can
see when it's undriven.
The plot of the "read" is at
http://www.bitwizard.nl/sdata.04.gif
and the postscript version is at:
http://www.bitwizard.nl/sdata.04.ps
If you want to make the plots yourself, the datafile is at:
http://www.bitwizard.nl/sdata001.gnuplot
and the gnuplot command (to get the area that shows me trying to read
the EEPROM) is:
plot [12300:13900] [20:130] 'sdata001.gnuplot' using 1 title 'SDA' w l, 'sdata001.gnuplot' using 2 title 'SCL' w l
So, my question is: Can someone who has experience with those i2c
EEPROMs take a quick look at my waveforms to tell me what I'm doing
wrong?
The datasheet for the 24lc256 is at:
http://www.bitwizard.nl/24lc256.pdf
and finally the source of the program that I'm using is at:
http://www.bitwizard.nl/test3.c
All help appreciated.
Oh, Before everybody tells me, there seems to be an extra start-stop
just before I start reading. I copied over some code I found on the
net, and I haven't yet cleaned that extra start-stop out of the code,
and as far as I can tell, it shouldn't matter...
Thanks in advance...
Roger.
--
** ####@####.#### ** http://www.BitWizard.nl/ ** +31-15-2137555 **
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