I2C help

i2c_confused

I am trying to communicate with an EEPROM chip (24FC515) using the bs2pe and it is not working.
The code I am using is as follows:

'{$STAMP BS2pe}
'{$PBASIC 2.5}
'{$PORT COM3}

sda PIN 0
current_ptr_b0 VAR Byte
address VAR Word
data_out VAR Byte
addr VAR Word


result VAR Byte

'The main loop

MainLoop:

GOSUB Init
GOSUB write_eeprom
GOSUB read_eeprom
DEBUG "Value read:",HEX result,CR
END


Init:

current_ptr_b0 = $00
data_out = $02
RETURN


write_eeprom:

I2COUT sda, $A0, current_ptr_b0, [noparse][[/noparse]HEX data_out]
DEBUG "writing Addr: ",HEX addr, " Value: ", HEX data_out, CR
PAUSE 2000
RETURN

read_eeprom:

I2CIN sda, $A1 , 0, [noparse][[/noparse]result]
DEBUG "reading Addr: ",HEX addr , " ", "Value: ", HEX result, CR
PAUSE 2000
RETURN


****************************************************************

The data that the stamp reads from the chip is always 1. I dont know why!

I am using 4.7k resistors and sda is connected to pin0.

Please help!

Bruce Bates

i2c_confused -

It appears from the data sheet that the ADDRESS must be 2 bytes (one WORD) in length. Thus, the ADDRESS in the I2Cxx commands will need to be specified in the "ADDRESS \ LOW ADDRESS" (separated bytes) format as shown in the PBASIC Help file, or the PBASIC Manual. In other words, something like this:

curr_ptr_b0 VAR WORD

I2COUT sda, $A0, curr_ptr_b0.highbyte\curr_ptr_b0.lowbyte, [noparse][[/noparse]HEX data_out]

and

I2CIN sda, $A1 , curr_ptr_b0.highbyte\curr_ptr_b0.lowbyte , [noparse][[/noparse]result]

Regards,

Bruce Bates

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Jon Williams

I've attached a file for you to try.··I don't have the part so I've not actually tested the program.· Please consult the data sheet for the 24LC515·for details.

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Jon Williams
Applications Engineer, Parallax

i2c_confused

Thank you for your help.

I used the code (with modifications for the 24fc515 chip).

I get a 'fail' output when I do this.

Also: the output that the stamp reads is '1'.

Any suggestions about what I might be doing wrong?

Jon Williams

You'll have to work through it as you have the chip and I don't. The first step is to review the data sheet -- I may have missed something. I can try to pick up a chip at the electronics store tomorrow, but there's no guarantee they'll have one.

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Jon Williams
Applications Engineer, Parallax

Bruce Bates

i2c_confused -

Do you have the Stamp and EEPROM chip wired as follows:

Stamp Pin Port 0 ==> SDA (EEPROM pin 5)
Stamp Pin Port 1 ==> SCL (EEPROM pin 6)

Vss (EEPROM pin 4) ==> Ground
Vcc (EEPROM pin 8) ==> 2.5-5.5 VDC

WP (EEPROM pin 7) tied to Vss
A2 (EEPROM pin 3) tied to Vcc

Regards,

Bruce Bates

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i2c_confused

Thanks for your help. I checked the wiring and it still doesnt work.

Could my stamp or eeprom be faulty?

·

Bruce Bates

i2c_confused -

My own guess would be the wiring or something external to the Stamp in some way is causing the problem, but that sounds terribly perjoritive - sorry. BTW - You get the continual 1's due to the required pull-up resistor I suspect.

Regards,

Bruce Bates

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Jon Williams

It is not likely that eithe your Stamp or EEPROM is faulty. As difficult as it may be for you to believe, this issues are always tied back to a bad or incorrect connection. Check your wires to make sure something is not broken.

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Jon Williams
Applications Engineer, Parallax

i2c_confused

I ordered in a new EEPROM chip and it still doesnt work!

I rewired everything- again, again and again.

Could the fact that my eeprom chip operates at 1MHz be a problem? Its really fast.... which seems to be a good thing in most cases I thought.

Any ideas about what I am doing wrong?

The input and output pins on the stamp are working. I tested them with an oscilloscope and with leds.

Jon Williams

Keep in mind that I2C is a syncronous buss and that 1 MHz number you're quoting is a maximum access speed. So... you've got a bad connection or bad code. Remember, the code I wrote was not tested by me; I wrote it for someone else who said that it worked fine. Once I get settled in my permanent home next week, I'll order a chip (couldn't find them locally) and test the code myself.

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Jon Williams
Applications Engineer, Parallax

i2c_confused

I am now testing my eeprom chip (sda and scl lines) using an oscilloscope.

So, for a write command, I get the following waveform:

1. Start bit. This is ok.

2. Then, the slave id which is 10100000 for a write, this is ok too.

3. Then,..... I need an ack bit. It is a low when the clock is high. BUT- I get a high when the clock is high. So my new eeprom chip is not sending an acknowledge bit. I have attached a waveform to show that.

4. The next byte is a 00000000 for the high byte of the address... so the high that I am seeing could not be the next byte either.

allanlane5

You DO have a common ground between the BS2 and the EEPROM, right? It doesn't look like it from the o'scope display.

i2c_confused

My eeprom ground is connected to vss, which is the stamp ground as well.

Post Edited (i2c_confused) : 2/25/2006 10:02:20 PM GMT

i2c_confused

So, I tried bit bashing and it works.

Conclusion: The i2cin/out does not work. HIGH and LOW commands work! So, I used bit bashing instead.

Here is an example of bit bashing that I modified to use:

http://www.lennard.net.nz/electronics/i2c.html#eepromexample.

Here is the waveform of the output using this code (see attached).

For some reason, my stamp is not working properly.

Bruce Bates

i2c_confused -

Approximately how old is this BS-2p? There are I2C differences between the 1.3 (I think that's the version level) firmware and earlier firmware versions. I happen to have one of the eariler versions, which I keep meaning to have updated with the newer firmware.

Regards,

Bruce Bates

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i2c_confused

I have the new BS2-pe. I ordered it about a month ago.