Internal Pull Resistors on GPIO

charles hill

Prodigy 140 points

Dear TI:

I am attempting to use the GPIO on the ezDSP which are brought out as test points (GPIO 21 thru GPIO 25)

In reviewing TI document # SPRS503A, Section 4.8.1 says that all GPIO pins are provided with internal pull up and pull down resistors.

I have tried configuring the test point pins to have internal pull resistors enabled. When I do so, I do not find the test point pins at 3.3 volt as I would expect. Instead, I find these pins at a few millivolts above ground.

I suspect that the SPRS503A document is in error and that the GPIO pins only have internal pull down resistors available.

Can you confirm that the C5505 has only pull down resistors available?

Thanks for the help!

Charles

over 15 years ago

0 Mark M over 15 years ago

TI__Mastermind 30110 points

Hello Charles,

We have a GPIO example on our eZdsp Google Code website that uses GPIO 21 and GPIO 22 as input and output, respectively.

Download “GPIO_Test1.zip” from http://code.google.com/p/c5505-ezdsp/downloads/list

I suspect that you are not properly setting the External Bus Selection Register (EBSR) that controls which set of multiplexed signals appear at the shared pins of the device. The GPIO[26:21] signals share pins with EMIF Address signals (EM_A[20:15] ). You will need to set each pin to show GPIO signals by setting each bit in EBSR[5:0] high (A20_MODE, A19_MODE, …, A15_MODE)

For information about the Pin Muxing and EBSR, see Section 7.3 Device Configuration in the VC5505 DSP System User's Guide (Rev. A).

Also see the C5505 General-Purpose Input/Output (GPIO) User's Guide.

In addition, we have CSL examples that perform GPIO input and output. Download "C55XCSL-LOWPOWER" from http://focus.ti.com/docs/toolsw/folders/print/sprc133.html

Hope this helps,
Mark

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