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TCA9539: questions of TCA9539

Jimmy Lai
Expert 6845 points
Part Number: TCA9539

Dear Team,

Questions are as follows,
Two TCA9539RTWRs are used in the design, and the IDs are 0x74 and 0x75 respectively. After power-on, use the MCU to read ID: 00~7F (reg is not specified), and all TCA9539RTWRs do not respond.
However, the MCU can R/W the specified reg for 0x74 to do R/W, but after R/W, go to read ID: 00~7F (without specifying reg), you can find 0x74, but 0x75 still does not respond,
The same steps, executed after 0x75, can also be found
Would like to ask if any special behavior is required to ack TCA9539RTWR in the initial?

Many Thanks,

Jimmy

  • 0
    TI__Guru 72181 points

    Hi Jimmy,

    Our I2C target devices which have multiple registers like the TCA9539 require a write transaction to the device to respond. An I2C detect (reading 00~7F) does an I2C read of devices but our devices require an internal register to be addressed before a read transaction can occur. If you modify your I2C detect to do a write to check for ACKs then it should work. 

    -Bobby