Regarding the built-in pull-up resistor when MSP430 IO is used as input!

火辣西米秀

Regarding the built-in pull-up resistor when MSP430 IO is used as input! [Copy link]

MCU: MSP430g2553 Evaluation Board
Software:
IARQuestion: Should I add a pull-down resistor when scanning a button with an msp430 microcontroller?
Description: Recently, when I was learning about TI's msp430 microcontroller, I wanted to test the onboard buttons, but I found that there was no pull-up resistor outside the IO. When I controlled P1.3 as input in the code, the IO was in a high-impedance state. I could change the potential of the IO by putting my hand on the IO. I naturally thought that I should add a pull-up resistor to the IO, but on the other hand, why didn't TI add a pull-up resistor when designing this board? Do they want us to add it ourselves? Unscientific! So I searched for related questions on the Internet, and many people added resistors separately. Am I overthinking? Suddenly I saw a blog, and the following is the content of the blog:
Today I helped someone test the msp430f2002, and he made such a request again, input, msp430 internal pull-up, and I habitually said, no, only output can be internally pulled up and down. He is a hardware engineer and is very skeptical. In fact, I am also skeptical.
I carefully read the datasheet of 430 and looked at the internal circuit. Wow, it's true. As a person with a major in telecommunications, I actually made such a conclusion without looking at the internal structure. I was careless.

Whether the pull-up or pull-down is enabled is determined by the REN register, and whether the pull-up or pull-down is enabled is determined by the OUT register. When used as an output, the pull-up or pull-down is automatically selected according to the high or low of OUT. When used as an input, we can also manually pay the OUT register to get the pull-up or pull-down.
After reading the above blog, I suddenly realized it! Thank you very much for the blogger's sharing! It helped me solve the problem! But I feel that the blogger's writing is not specific enough. In order to make everyone understand, I will add it again!
As the blogger said:
The PxREN register controls whether the pull resistor is enabled, and PxOUT determines whether the pull resistor is pulled up or pulled down. The specific working principle is as follows:
When PxDIR=1, the output is PxREN=1. Only the pull resistor works. PxOUT=1 pulls up.
PxOUT=0 pulls down.
PxREN=0 push-pull output has no pull resistor. PxOUT=1 outputs high.
PxOUT=0 outputs low.
When PxDIR=0, the input is PxREN=1. The pull resistor works. PxOUT=1 pulls up.
PxOUT=0 pulls down.
When PxREN=0, the IO is in a high-impedance state. High-impedance state

#include<msp430g2553.h>
void main()
{
WDTCTL=WDTPW+WDTHOLD;
P1DIR=0x0001;
P1REN=BIT3; //input
P1OUT=BIT3; //pull
upwhile(1)
{
if(P1IN&BIT3)
P1OUT|=BIT0;
else
P1OUT&=~BIT0;
}
}
I hope this helps!