DS90UB948-Q1: how to disable back channel?

Dai Xinyu

Prodigy 70 points

Part Number: DS90UB948-Q1
Other Parts Discussed in Thread: USB2ANY

We use ub941->ub948. Now we want to disable back channel for test eye diagram. How to disable back channel?

over 3 years ago

0 Hamzeh Jaradat over 3 years ago

TI__Guru** 107510 points

Hello Dai,

to Disable the back channel you need to make sure that reg 0x01[2] is set to 0, additionally the I2C pass through bits, 0x03[3] and 0x05[7], are also set to 0.

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

0x01[2] doesn't use in my ub948 datasheet.It is reserved.

My ub948 0x3[3] and 0x5[7] have set to 0 already.

It doesn't look like disable success. 941 also can communicate with 948 in i2c and gpio.

0 Hamzeh Jaradat over 3 years ago in reply to Dai Xinyu

TI__Guru** 107510 points

As said, all three bits must be set to 0.

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

But 0x01[2] is read only. I read 0x01 register is 0x4.And I try to write 0 to it . It doesn't change.

0 Hamzeh Jaradat over 3 years ago in reply to Dai Xinyu

TI__Guru** 107510 points

You need to write locally not remotely, i.e. use the 948 local I2C bus for changing this register.

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

How to use 948 local I2C? I only can write it through 941 now.

0 Hamzeh Jaradat over 3 years ago in reply to Dai Xinyu

TI__Guru** 107510 points

You need to have access to the 948 Board I2C. Otherwise it is not possible to disable the back channel.

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

Do you have any tools to write it?

0 Hamzeh Jaradat over 3 years ago in reply to Dai Xinyu

TI__Guru** 107510 points

You can use any I2C tool such as Aardvark or USB2ANY or any programming tool.

0 Hamzeh Jaradat over 3 years ago in reply to Hamzeh Jaradat

TI__Guru** 107510 points

Dai,

If you want to measure the forward channel Eye-Diagram, you can unplug the cable from the DES board and then measure the Eye-Diagram. You do not need to disable any back channel.

Alternatively, you can connect your scope to the CMLOUT pins on the 948 and measure the Eye-Diagram.

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

There are any problems in my eye-diagram. So I want to disable back channel to try can it be ok.

Can you help me with other question?

e2e.ti.com/.../ds90ub948-q1-eye-diagram-freq-is-wrong

+1 Hamzeh Jaradat over 3 years ago in reply to Dai Xinyu

TI__Guru** 107510 points

Hello Dai,

Please try to power down the back channel by setting 0x63[1] = 1

the other thread is assigned to my colleague

0 Dai Xinyu over 3 years ago in reply to Hamzeh Jaradat

Prodigy 70 points

Thanks. I try it and disable back channel successful.

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DS90UB948-Q1: how to disable back channel?