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TCA9548A / I2C standard

Sho Ogane
Genius 5575 points

Other Parts Discussed in Thread: TCA9548A

Hi all.

I have two question about TCA9548A.

1.Datasheet P.14 8.5.3.1 Writes
I can't understand the followimg sentense.
"There is no limit to the number of bytes sent, but the last byte sent is what will be in the register."
What is last byte?

2.Datasheet P.16 8.5.4 Control Register
We need to send stop condition after the acknoledge cycle.
・What is the acknoledge cycle?
・Does MCU have to send stop signal after control register everytime ? 

Best Regards,
Sho Ogane

  • 0
    TI__Expert 5140 points

    Hi Sho,

    Thanks for the question.

    1. What is the last byte?

    The sentence is stating that you can continuously write several or more commands to that register that will take effect; however, the last byte that is sent is what will be stored within the register.

    2. What is the acknowledge cycle

    The acknowledge cycle refers to the slaves acknowledging the slave address, control register being written/read to. With this in mind, once these are completed, the master will need to provide a NACK before sending the STOP condition.

    3. Does the MCU send the stop signal after the control register every time?

    Please refer to the image below:

    From what is shown, the Master is performing the commands in GRAY while the slave is performing what is in WHITE. In this case you are correct that the MCU must send the STOP condition every time.

    Thanks,

    Siby

  • 0 in reply to Siby James
    Prodigy 10 points

    Dear TI,

    I have a question about the I2C communication protocol to write and send trough the TCA9548A.
    In example (picture) I pickt write protocol.

    1)
    In 8.5.4 Control Register I read " When a channel is selected, the channel becomes active after a stop condition has been placed on the I2C bus."
    So after each start and command byte I must stop the I2C communication to activate CHx.

    Will I send before every data a command byte or one time? 

    2)
    8.5.4 Control Register "If multiple bytes are received by the TCA9548A, it saves the last byte received."

    8.5.3.1 Writes "There is no limit to the number of bytes sent, but the last byte sent is what is in the register.

    If I used protocol.

    start write
    command register CH0
    databyte 0x70
    databyte 0x66
    stop

    Witch databyte is in my register?
    I think nothing becaus the command register isn't active.

    3)

    Question about page 8, figure 15 from www.sensirion.com/.../Sensirion_Humidity_Sensors_SHT21_Datasheet_V4.pdf

    in combination with the TCA9548A

    Is it posible to give a full example to send one read register byte for slave channel 0.
    Slave channel 0 reacts by sending two bytes data, that need to be read.

    Please give the example with the TCA9548A START, ADRESS, R/ ~W, CONTROL REGISTER, DATA (write/ read), (N)ACK, STOP

    4)

    Is it posible to give an example of two or more bytes sending to a channel?