TCA9546A: Control Register/Channel Selection

Brian Cox

Part Number: TCA9546A

Trying to enable each of the 4 output channels on the TCA9546A.

Sheet 14 appears to be the relevant section of the datasheet: https://www.ti.com/general/docs/suppproductinfo.tsp?distId=10&gotoUrl=https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Ftca9546a

My A2, A1 and A0 pins are all tied low in hardware.

Refer to the attached scope shot.

After the initial write, I write 11100000, which should corespond to the fixed slave address and the state of those 3 pins.

Then I write 00001111. The first 4 bits are don't cares and the 4 ones should enable all 4 channel outputs.

However, I still can't get anything out of any channel with any subsequent writes.

Is there another subsequent or prior write I have to do? What could I be missing?

Thanks.

over 3 years ago

0 Chris Ayoub over 3 years ago

TI__Genius 15345 points

Hi Brian,

What is the first command that you are sending? The 10100000.

Best,

Chris

0 Clemens Ladisch over 3 years ago

Guru 318920 points

In the capture shown above, the slave address is 1010000.

To access the TCA9546A, the slave address must be 1110000, and you must write only one data byte.

0 Brian Cox over 3 years ago in reply to Clemens Ladisch

Prodigy 20 points

Thanks I will look into where that command is coming from, but you will see the next command that gets sent is 11100000. Why doesn't that do anything?

0 Clemens Ladisch over 3 years ago in reply to Brian Cox

Guru 318920 points

The first byte in an I²C transaction contains the slave address and the R/W bit. All following bytes, up to the stop condition, are handled by the addressed device. In the capture shown above, that device is not the TCA9546A.

0 Chris Ayoub over 3 years ago in reply to Clemens Ladisch

TI__Genius 15345 points

Yes, as Clemens is saying you are accessing another device on the bus. Any I2C device with internal registers will first expect to see it's address after a start bit. That is how it knows the controller is talking to it. If you send something that isn't the address after the start bit the I2C device will ignore it.

Best,

Chris

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TCA9546A: Control Register/Channel Selection