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PCA9545A Address

SHIVENDRA MISHRA
Prodigy 50 points
Other Parts Discussed in Thread: PCA9545A, TCA9545A

Hello folks!
I've few basic question about the circuits attached:

1) Why are we grounding A0 and A1? Is it defining the address of PCA9545A  ic address? What if, I'm attaching 2 such IC on bus? If i want to send data to sd0, SD1?

2) If i don't have INT supported on sensors(slave) and Master; Should i attach all INT pins to Vcc?
3) If I use Vcc = 5V; Is it going to effect my transmission somehow; when compare to Vcc - 3.3v?

Thanks in advance.

  • TI__Mastermind 30280 points

    1) Yes, A0 and A1 define the I2C slave address of the PCA9545A. If they are both tied to GND, the slave address is 0xE0 for Write/0xE1 for Read.

    If you have 2 PCA9545A parts on the same I2C bus, then you may follow the application diagram for one of the parts (GND both A0 & A1) and for the other PCA9545A you can pull-up both A0 & A1 to VCC using ~100k resistors to make the slave address 0xE6/7 (W/R).

    Please ensure that you have no conflicting I2C addresses on either of the buses, because you can also set A0=GND and A1=VCC or A0=VCC and A1=GND.

    See the "Control Register" section of the datasheet (p. 5) to learn about how to write to the devices attached to each channel.

    2) If you are not using the /INT pins, it would be best to tie them to GND. (If you tie them to VCC, it will waste current if the /INT becomes activated for some reason). These are open-drain I/O output structures.

    3) There are many differences between using VCC=3.3 V vs. 5 V. You can determine if these differences are a problem by reading the Electrical Specs for both voltages and reading the "Voltage Translation" section of the datasheet (p. 7).

    Also, there is an errata on the PCA9545A about POR. The TCA9545A is scheduled for release late Feb./early March in 2014 and it will resolve the POR issue.

    Thanks,

    Brian

  • in reply to Brian Berner
    Prodigy 50 points

    Answer 1) : Got it. Thanks.

    Answer 2):  I've connected pull up resistors to Vcc. and data sheet says to connect unused INT to Vcc. So, i've connected these INT0 to 3 to Vcc.

    Answer 3): Got it. Thanks.

    -----------------------------------------------------------------------------------------------------------------------------------------------------
    Finally, my circuit doesn't work.

    This is what, I've done overall:

    a) Vcc = 5v; 

    b) 4k7 pull up resistor on master SDA and SCL attached to Vcc. (Master = ATmega2560, 5V mc)

    c) Reset to Vcc through a push switch. (Push=GND; Release=Vcc)

    d) Channel 0 and 1: 4K7 connected to 3.4V for MSP430 G2553 (on both channel).

    I'm using SLA383 application note. and changed TXDATA = 0x0f. and made lines of   void receive_cb() as comment. (Trying to send 0x0f to master). 

    I also tried to change slave address as 0x00 and 0x01. (Is it required?)

    I don't see any clock on SC0 or SC1 or SCA. and no changes over SD0 or SD1 or SDA.


    Any idea, how should i check this whole setup ?

    Any advice will be appreciated.
    Thanks in advance.