PCA9548A: Please let me know how to describe I2C address and data.

Makoto Teramoto

Part Number: PCA9548A
Other Parts Discussed in Thread: BQ76940,

Hi team,

I would like to communicate a MCU and AFEs(bq76940 x 6) via PCA9548A. Would you let me know how to describe address and data?
I have refered the datasheet and slva704.pdf. My idea is as follows. Is that OK? (In case of A0-A2 = 0 and B1 is selected.)

- Write
0b00010000 - 0b11100000 - 0b00000010 - (data to write)

- Read
0b00010000 - 0b11100001 - 0b00000010 - (data to read)

Regards,
Makoto Teramoto

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 317170 points

You are showing three bytes. But an I²C transaction to the PCA9548A has only two bytes, the address/R/W byte, and the control register value.

Without that first 00010000, these would be correct.

0 Makoto Teramoto over 3 years ago in reply to Clemens Ladisch

Intellectual 295 points

Hi Clemens,

Thank you for your quick answer !
The first one is a slave address of AFE, as you know. Does that not be needed?

Regards,
Makoto Teramoto

0 Clemens Ladisch over 3 years ago in reply to Makoto Teramoto

Guru 317170 points

The PCA9548A itself is an I²C device. When configuring the switches, you address it alone.

The switches create a direct electrical connection. You address downstream devices normally, as if the switch were not there.

0 BOBBY over 3 years ago in reply to Makoto Teramoto

TI__Guru 73491 points

Hi Makoto,

As Clemen's pointed out, the 9548A device is an i2C operated switch. You simply send the device address of the 9548A with a write bit set then send one more byte to set the channel you want to enable. After that you must do a stop condition, at that point the I2C switch should have enabled the channel you set. From there you would just communicate normally with the downstream device on that enabled channel normally. When you need to switch channels you would then just write to the device address of 9548A and set the next channel you want to communicate downstream with and issue a stop condition.

-Bobby

0 Makoto Teramoto over 3 years ago in reply to BOBBY

Intellectual 295 points

Hi Clemence and Bobby,

Thank you all ! I understand the mechanism.
I will try it later. (Maybe next week, with new substrate.)

BTW, there is "8.6.3.2 Reads" explanation in datasheet.
Is that how to read the condition of the PCA9548A itself? I guess so, but just in case.

Regards,
Makoto Teramoto

0 Clemens Ladisch over 3 years ago in reply to Makoto Teramoto

Guru 317170 points

Yes, section 8.6.3.2 shows how to read the PCA's control register.

0 Makoto Teramoto over 3 years ago in reply to Clemens Ladisch

Intellectual 295 points

Thank you Clemens.
Your answer is always quick !

I close this question. Thank you again !

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PCA9548A: Please let me know how to describe I2C address and data.