OMAP Default Internal Pullup/Pulldown

Colin Koo

Other Parts Discussed in Thread: OMAP-L138

I'm a little confuse with the default IPU and IPD when working on the OMAP-L138 processor. The OMAP pins are classified according to pin groups such as CP[0], CP[1], CP[2], etc... Thse pin groups are configurable to be internally pulled up or pulled down. However, immediately coming out of reset, there's a default setting assigned to them.

According to the OMAP-L138 Application Processor System documents, only pin groups CP[26], CP[27], CP[28] and CP[29] will be internally pulled down while all other pin groups will be internally pulled up. However, this is not what i seen. I notice that pin GP1[15] in pin group CP[4], which is suppose to be pulled up is pulled down instead. Another case is that pin GP7[12] in pin group CP[28], which is supposed to be pulled down is pulled up.

Does this kind of thing happens often? Is it the case that the default pull ups/downs would not necesarily follow what the document states? Does that mean we should always use strong pull ups/downs (~1kohm) on those lines which is intended to have a default logic even though it is stated in the document whether it is internally pulled up or down?

Hope someone can help advise.

Thanks.

Regards

Colin

over 14 years ago

0 dabuan over 14 years ago

TI__Genius 14545 points

Colin,

Sorry for the delay. Did you see the note associated with the Pull Up/Down Select Register?

FYI: We've combined the System Reference Guide and all the Peripheral User Guides into a unified Technical Reference Manual. So if you are looking for the System Reference Guide, it will not be located in the TRM.

0 Colin Koo over 14 years ago in reply to dabuan

Prodigy 80 points

Thanks for responding. That's what I'm trying to explain. According to the Pull Up/Down Select Register (PUPD_ENA) in the Application Processor System document, it mention that pin group CP[26], CP[27], CP[28] and CP[29] are pulled down by default after reset and the rest are pulled up. however, that's not exactly what i saw. I have a few OMAP where one of it would have a pull up on some of those pins in CP[26], CP[27], CP[28] and CP[29], which is supposed to be pulled down. And some other boards having pull down on other pins which are supposed to be pulled up. Is these kind of stuff common? Or should it be something that shouldn't happen?

Thanks

Regards

Colin

0 Milan Zelenka over 12 years ago in reply to Colin Koo

Intellectual 870 points

Colin,
Have you ever got an answer?

Milan

0 BrandonAzbell over 12 years ago in reply to Milan Zelenka

TI__Guru 64500 points

Please take a look at Advisory 2.1.23 in the silicon errata document found on the product folder for the OMAP-L138.

0 Milan Zelenka over 12 years ago in reply to BrandonAzbell

Intellectual 870 points

The advisory addresses CP29 only.

Colin reported other issues.

Please confirm or reject reported issues.

0 Raja over 12 years ago in reply to Milan Zelenka

TI__Guru* 81335 points

Please refer thread on OMAP-L138 Internal Pulls:

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/t/278980.aspx

Thanks.

0 Milan Zelenka over 12 years ago in reply to Raja

Intellectual 870 points

Hello Rajasekaran,
for some unknown reason you are trying to navigate me to a thread that is not relevant to my question. Let me repeat my query again.

Colin reported some issues with internal pulls. Try as I may I can't find any feedback from TI.

Please confirm or reject the reported issues. I need t know whether the datasheet spec is valid or not. At the moment, the only confirmed PMAP-L138 design issue I am aware of is CP[29] - BOOT pins.

Many thanks in advance,
Milan

0 Raja over 12 years ago in reply to Milan Zelenka

TI__Guru* 81335 points

Hi Milan,

Sorry for the trouble. We have escalated your query to the development team.

And also I felt that the link to your verified thread (OMAP-L138 Internal Pulls) will be helpful if someone else referring this thread.

Thanks.

0 Mukul Bhatnagar over 12 years ago in reply to Milan Zelenka

TI__Guru* 83965 points

Hi Milan

The post from Collin is ~ 2 yr old. I believe at that point there might have been some issues with clarity in the documentation.

The issue with CP29 group alone was captured in the errata. There are no additional outstanding issues on this topic.

The foot note in the datasheet, clarifies the behavior of the pins during and after reset.

Let us know if you have any specific concerns or observations that are causing a concern.

Regards

Mukul

Datasheet footnote

IPD = Internal Pulldown resistor; IPU = Internal Pullup resistor; CP[n] = configurable pull-up/pull-down (where n is the pin group) using the PUPDENA and PUPDSEL registers in the System Module. The pull-up and pull-down control of these pins is not active until the device is out of reset. During reset, all of the pins associated with these registers are pulled down. If the application requires a pull-up, an external pull-up can be used. For electrical specifications on the pull-up and and internal pull-down circuits, see the Device Operating Conditions section.

0 Milan Zelenka over 12 years ago in reply to Mukul Bhatnagar

Intellectual 870 points

Thanks Mukul.
No more questions.
Milan

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OMAP Default Internal Pullup/Pulldown