External EEPROM can't read/write

[coyotegd]

Darrel, I started this mess with a word sized address without highbyte, lowbyte. I found in another thread that the high-low byte addressing worked for someone, and when it didn't work for me, I made my first post in this tread with my code at the time.

However, I changed the 16F877 a third time and it's working! Is it possible that some PICs just don't work with I2C? Prior to finding a working 16F877, I tried two other 16F877's and a 16F876A. All failed to work properly.

Is it possible I had the circuit wrong? I can't go back and try a PIC that failed because they are all in their respective parts' bins with others of the same type. The most complicated part of my circuit is the MAX233, and it worked properly the first time. The 24LC256 is simple: Pins 1 to 4, and 7 to gnd, pin 8 to 5V, pin 5 pulled-up and to c.4, and pin 6 pulled-up and to c.3.

Anyway, thank you all. You kept me motivated to keep trying. All I can say to anyone reading this tread with a similar problem is just keep trying different components, and periodically, start your breadboarding all over again. As stated above I tried four different PICs, and I re-wired my circuit at least four times. This is the code that works:

@ DEVICE HS_OSC, WDT_OFF, LVP_OFF, BOD_OFF, PWRT_OFF, PROTECT_OFF

DEFINE	LOADER_USED	1
DEFINE    OSC 20
addr      var       word
edata     var       BYTE
addr = 0
edata = 50
pause 100
for addr = 5 to 10
     I2CWRITE portc.4,portc.3,$A0,addr,[edata],Nowriteack
     pause 10
     serout2 portc.6,32,[dec addr,44,32,dec edata,10,13]
     edata = edata + 10
next
for addr = 5 to 10
     i2cread portc.4,portc.3,$A0,addr,[edata],NoREADAck
     serout2 portc.6,32,[dec addr,44,32,dec edata,10,13]
next
end
NoWriteAck:
serout2 portc.6,32,["No Write Acknowledgement",10,13]
return
NoReadAck:
serout2 portc.6,32,["No Read Acknowledgement",10,13]
return

I've attached a picture, which was the objective of this exercise. It's rough, but at least I can move on to improvements and new challenges.

[Darrel Taylor]

... I tried two other 16F877's and a 16F876A. All failed to work properly. ...
I can't go back and try a PIC that failed because they are all in their respective parts' bins with others of the same type.

Is it possible that some PICs just don't work with I2C?

I doubt that very strongly.

But, I would imagine that putting parts that have had problems back in the bin with the new chips, would enhance the probability considerably.

Anyhow, glad it's working.

Cheers,

Added: Woohoo! Nice picture.

[Michael Wakileh]

In the past I've had a lot of sporadic problems with i2c and breadboards as well...I suspect your problem was solved somehow when rewiring the breadboard... My problems always went away when soldering my prototypes... Hope this helps...