cc2541 input with pull-down

pietro miotto

I’m a beginner with electronics and I’m currently trying to work out how to set a pin with internal pull-dow resistor?

As per spec sheet, an input pin is by default set with a pull-up resistor, I need to change P0.0 to be input with pull-dow resistor

P0SEL = 0;

P0DIR = 0xFE; // Port 0 pins P0.0 as input, all others as output

P0 = 0x01; // All pins on port 0 to low except for P0.0

Any help would be appreciated

over 10 years ago

0 YiKai Chen over 10 years ago

Guru 735685 points

If you want to set P0.0 to GPI with pull-down, you have to set bit 5 of P2INP to 1. You can refer to CC2541 user guide.

0 pietro miotto over 10 years ago in reply to YiKai Chen

Intellectual 270 points

Is there a code example?

Only need P0.0 to input with pull-down, everything else to output low .

0 YiKai Chen over 10 years ago in reply to pietro miotto

Guru 735685 points

Please refer to the following codes

P0SEL = 0x0; //Select all pins on P0 as GPIO
P0DIR = 0xFE; //Set P0.0 as GPI and others as GPO
P2INP |= BV(5); //Set P0.0 to pull-down
P0 |=0x0; //Ouput P0.1 ~ P0.7 to low.

0 pietro miotto over 10 years ago in reply to YiKai Chen

Intellectual 270 points

This is great, makes sense now.

Just so I fully understand:

1. To set all port 0 to pulldown, bit 5 of P2INP is set to 1 by P2INP |= BV(5). How do I set bit 5 to 0?

2. "P0 != 0x0" won't this set P0.0 also to low?

Sorry about these stupid questions, i'm new to bitwise operators

0 YiKai Chen over 10 years ago in reply to pietro miotto

Guru 735685 points

1. To set bit 5 to 0, you can use P2INP &= (~BV(5))

2. P0.0 already set to GPI so it won't output to low.

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cc2541 input with pull-down