AM335x Internal Pullup Help

Sundeep Dhunna

Other Parts Discussed in Thread: SYSBIOS

I can't seem to get the internal pull-ups working. I perform a pin mux, then set the direction, however when I run the code the pin that I am expecting to be pulled up remains at the value of 0 after a restart. The pin is not connected to anything.

I use PinMuxConfig from plat_mux.c and these are the settings:

{ PIN_GPMC_AD0 , PIN_MODE(7) , (PIN_PULL_TYPE_SEL | PIN_RX_ACTIVE) & (~PIN_PULL_UD_EN)}

And then I set the direction:

GPIODirModeSet(SOC_GPIO_1_REGS, 0, GPIO_DIR_INPUT);

To read the pin:

GPIOPinRead(SOC_GPIO_1_REGS, 0))

One more thing. If I connect the pin to logic high, read it, and then disconnect it and read the pin, the pin value stays at 1.

over 11 years ago

0 Yordan Kovachev over 11 years ago

TI__Guru**** 161600 points

Hi Sundeep,

Which SDKI version are you using?

Have you checked if the PIN_GPMC_AD0 is used for another purpose by u-boot?

Best Regards,
Yordan

0 Sundeep Dhunna over 11 years ago in reply to Yordan Kovachev

Prodigy 160 points

It is running TI SYSBIOS. (bios_6_40_04_47 and am335x_sysbios_ind_sdk_1.1.0.6) on the ICE_V2 evaluation board.

I don't see any other uses for this pin and since I'm using sysbios there is no u-boot. I have checked the contents of the control register for this pin using the CCS debugger and the flags appear to be correctly configured for pull-up.

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

Sandeep,

Sundeep Dhunna said:
One more thing. If I connect the pin to logic high, read it, and then disconnect it and read the pin, the pin value stays at 1.

What is the behavior that you expect with an internal pullup enabled? This is exactly as it should be.

0 Sundeep Dhunna over 11 years ago in reply to Biser Gatchev-XID

Prodigy 160 points

Pin disconnected - high
Pin connected to ground - low

In the last line of my post I tried to point out that the value appears to be buffered somehow.
1) Connect pin to logic low, it is read as 0
2) Disconnect pin, it is read as 0 (should be 1)
3) Connect pin to logic high, it is read as 1
4) Disconnect pin, it is read as 1 (expected behaviour, but seems like value is being retained)
5) Connect pin to logic low, it is read as 0
6) Disconnect pin, it is read as 0 (should be 1)

0 Biser Gatchev-XID over 11 years ago in reply to Sundeep Dhunna

TI__Guru**** 393215 points

How do you read the GPIO value? In a cycle? Do you have some delay between consecutive reads? Can you post the code fragment?

0 Sundeep Dhunna over 11 years ago in reply to Biser Gatchev-XID

Prodigy 160 points

After looking at the schematic, I found that the pin was also connected to other hardware on the eval board (Flip Flip & Nor flash) in addition to the pin header. The other hardware probably caused the behaviour I was seeing.

I tried a different pin and the pull-up works as expected.

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AM335x Internal Pullup Help