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PCA9955 LED driver interface problem with ATmega128

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sujan_014

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I am trying to interface PCA9955 with ATmega128. I connected address pin A0, A1, A2 and A3 to ground and used device address 0xC0 to communicate using I2C. The I2C code is verified as I have used the same code to communicate with other I2C device.. Despite this, PCA9955 does not acknowledge when device address, register address or data is sent. Can any one tell me what is problem here ?
ckt_t.jpg

This is my circuit.
 

Can you probe on the SCL & SDA lines and verify it is toggling? What speed I2C clock is operating? Try to reduce the clock and try.
 

Yes, the SCL and SDA lines are also toggling when data was sent. I checked through oscilloscope. The I2C speed is 1000Hz. I think that the problem lies in this hardware but so far I don't know where it is !
 

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