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The PCA9698 I2C I/O port expansion controller datasheet shows that 64 slave devices are addressable via 3 address input signals using VDD, VSS, SCL and SDA as the possible connections. How does this work to use active bus interface signals as the inputs

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The PCA9698 I2C I/O port expansion controller datasheet shows that 64 slave devices are addressable via 3 address input signals using VDD, VSS, SCL and SDA as the possible connections. How does this work to use active bus interface signals as the inputs

‎08-10-2017 06:44 AM
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jameydobbins
Contributor I

see attached datasheet for the PCA9698

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‎08-14-2017 12:13 AM
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TomasVaverka
NXP TechSupport
NXP TechSupport

Hello Jamey,

The PCA9698 has three address pins AD0/AD1/AD2.
Only using a binary logic (Vdd or Vss) would limit the possibility to only 8 PCA9698 on the same I2C bus. 
By using SCL & SDA also as address decoding allows to increase the number of PCA9698 up to 64 per I2C bus. 
The position from the address inputs AD0/AD1/AD2 get sampled once of ever during the Power On Reset (POR) sequence. As a consequence, SDA and SCL state changes after POR have no influence on addressing.

Best regards,

Tomas

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