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Kosta
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| Help Please...External EEPROM chip never responds |
 Posted: Tue Apr 27, 2004 12:34 pm |
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Hi Everyone,
I am trying to use a 24c00 chip along with my PIC16c771 to implement I2C bus for the storage of variables.
For some reason the EEPROM chip never ACKs any of the commands sent by the micro. I'm attaching a picture of a waverform that tries to write a byte of data to the EEPROM chip. As you can see, first there is a start condition, then the control byte 1010xxx0. But after the control byte, the EEPROM chip is supposed to ACK and it never does.
Do any of you see anything wrong in the waveform?
The Green is SCL, Yellow is SDA.
Thanks |
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fpgeh
Joined: 07 Sep 2003
Posts: 19
Location: Vancouver, BC
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| Posted: Tue Apr 27, 2004 12:42 pm |
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Your rise times look a bit long. You can probably reduce the size of the pullup resistors. With the time div. you have set (25us) it looks like your rise times could be near 5us. The spec sheet gives a max rise time of 1000ns.
Also, how many devices are on the bus? If there are a lot, then bus capacitance will be high resulting in longer rise times. |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Tue Apr 27, 2004 12:47 pm |
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| Do you have pull up resistors on the SDA and SCL lines? |
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Kosta
Guest
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| Posted: Tue Apr 27, 2004 12:57 pm |
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Yes I do have pull up resistors on both the signals.
I tried to reduce them from 10k to 2.4K just now.
The rise time became much smaller and the signals looked almost like perfect square waves but still the EEPROM chip isn't responding.
And I just have a master and slave on the I2C bus so capacitance from that should not be an issue. |
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fpgeh
Joined: 07 Sep 2003
Posts: 19
Location: Vancouver, BC
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| Posted: Tue Apr 27, 2004 4:41 pm |
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| From your pic, the I2C signals look correct. Are you sure SCL and SDA aren't swapped? Did you check the power connections? And have you tried another EEPROM chip? Maybe one burned out. |
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rnielsen
Joined: 23 Sep 2003
Posts: 852
Location: Utah
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| Posted: Wed Apr 28, 2004 8:26 am |
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| Are you using the built in I2C functions or are you trying to 'bit bang' the signals? Maybe if you posted a bit of your code it might help too. |
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Kostik
Guest
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| Posted: Wed Apr 28, 2004 9:40 am |
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I checked the lines and they are connected properly. I will also try a different chip.
I'm using the built in functions. My compiler is pretty old v. 3.056. I don't know if that makes a difference or not.
Here's a bit of my code. Maybe you might see something wrong in it.
It is just a snip of it so not everything, like the main loop, defines, etc. is included.
| Code: |
#include <16C771.h>
#device ADC=12
#use delay(clock=4000000)
#fuses XT,NOWDT,BROWNOUT
#use i2c(MASTER, FORCE_HW, FAST, SCL=PIN_B2, SDA=PIN_B4)
// following just runs once
output_float(PIN_B2);
output_float(PIN_B4);
write_eeprom(BYTE_ADDR1, 0xF8);
void write_eeprom(byte address, byte data) {
int ack = 0;
i2c_start();
ack = i2c_write(0xa0);
ack = i2c_write(address);
ack = i2c_write(data);
i2c_stop();
delay_ms(11);
}
byte read_eeprom(byte address) {
byte data;
i2c_start();
i2c_write(0xa0);
i2c_write(address);
i2c_start();
i2c_write(0xa1);
data=i2c_read(0);
i2c_stop();
return(data);
}
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Thanks! |
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Kostik
Guest
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| Posted: Wed Apr 28, 2004 12:20 pm |
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Guys it was a bad EEPROM chip.....
Thanks for all the help. |
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