TMS320C6748 GPIO pullup and pull down configuration

Vinay Manikkoth

Prodigy 120 points

Hi,

I want to enable internal pull down resistor during reset/bootup. how ca i do this

Thanks

Vinay

over 9 years ago

0 Titusrathinaraj Stalin over 9 years ago

TI__Guru** 116100 points

Hi Vinay,
You can enable internal pullup/down through "PUPD_ENA" and "PUPD_SEL".
Please refer to the C6748 TRM, page no 281.

www.ti.com/.../spruh79a.pdf

0 Vinay Manikkoth over 9 years ago in reply to Titusrathinaraj Stalin

Prodigy 120 points

Hi,

what will be the status of IOs when there is a power up. by default pullup? in any way i can make it pulldown?

Thanks

Vinay

0 Senthilkumar Srinivasan over 9 years ago in reply to Vinay Manikkoth

TI__Mastermind 43660 points

Hello Vinay,

The internal pull up / pull down resistor on IO pins that are active by default after a power-on reset. You can look in the "Terminal Functions" section of the data sheet to see the pins group.

This can be changed at run-time by modifying the PUPD_SEL register as documented in the TRM section 10.5.22. You can also find the default values of IO groups upon reset in table 10.54.

Regards,
Senthil

0 Vinay Manikkoth over 9 years ago in reply to Senthilkumar Srinivasan

Prodigy 120 points

Hi,

I have an external pulldkown which i need for my design( i cannot change this). while power up i can see that, voltage in this goes into a intermediate level till the processor come out of reset. i guess this is happenig because of an internal pullup. i want to disbale pullup, so that my signal will be in valid state till the processor come out of reset. is this possible?

Thanks

Vinay

0 Senthilkumar Srinivasan over 9 years ago in reply to Vinay Manikkoth

TI__Mastermind 43660 points

Hello Vinay,

Yes, you can disable internal pullup/pulldown in PUPD_ENA register. Please look into the section 10.5.21 Pullup/Pulldown Enable Register (PUPD_ENA) in the TRM.

Regards,
Senthil

0 Vinay Manikkoth over 9 years ago in reply to Senthilkumar Srinivasan

Prodigy 120 points

HI,

it clearly says that, these settings will not come into effect till the processor come out of reset.

for more clarity, let me divide the entire process into 3 sections.

1. No power
2. Boot up time (booting from external flash. this take about 2 sec)
3. powered

what will be the GPIO state during 2nd section. during this time, one of GPIO goes into 1.25V. i have a 10K pulldown (external). i doubt there is an internal pull up.

when i tried to change this to pulldown by accessing the PUPD_SEL registers, it go to zero only after coming to 3rd section.

is it possible to enable pull down while section 2 instead of pullup

Thanks
Vinay

0 Titusrathinaraj Stalin over 9 years ago in reply to Vinay Manikkoth

TI__Guru** 116100 points

Hi Vinay,
What is the purpose of this pin that you need to pull down ?
This pull down functionality need while bootup ?

We may need like IBL (intermediate bootloader) for your requirement.
IBL code must be to configure the pull down mode through PUPD_SEL register.

You would get expected behavior on that pin after IBL stage.

As Senthil said, while bootup, the pin would hold the default PULL UP/DOWN value.

0 Vinay Manikkoth over 9 years ago in reply to Titusrathinaraj Stalin

Prodigy 120 points

Hi,

yes this pin should be low while bootup.

How can i know more about IBL? any reference documents

Thanks
Vinay

0 Titusrathinaraj Stalin over 9 years ago in reply to Vinay Manikkoth

TI__Guru** 116100 points

Right now, do you have any bootloader before running your actual application ?
If not, please create a tiny bootloader ('C' code) where you need to set/configure the pull down mode through PUPD_SEL register with your actual application entry.
So that after tiny bootloader, the original application would call and execute on DSP core.

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TMS320C6748 GPIO pullup and pull down configuration