A Pullup Resistor brings a line up to a voltage (Typically VCC), while allowing the line to be pulled low.

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1answer
71 views

SPI bus termination and pull-up resistors

My microcontroller (ATMEL series) needs to communicate to a slave device using SPI protocol. I am designing the hardware. The maximum SPI bus speed is 1 MHz. The distance between the master and slave ...
3
votes
2answers
91 views

Why do we use pull up resistor with PIC?

I tried to find an appropriate answer for the question but couldn't find what I needed exactly. I found out that "Initially the output from the PIC is floating and we use the pull up resistor R7 to ...
0
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0answers
32 views

BeagleBone GPIOs mode

I want to know what is the mode of BeagleBone white pin if I use it as an input, is it pull-up or pull-down or have both or what exactly, I am a little confused, I had read that it is pull-down and ...
0
votes
2answers
52 views

How to detect pin state change in pulled up pins

I am working on Toradex module and developing a simple application where I am detecting the input and displaying it on UART. Now the application requirement is that we give 12v as input but the ...
1
vote
1answer
93 views

Why do we need a pull-up resistor when there is a floating connection at the base of a transistor?

Let's say that the base is connected to any normal PIC. My teacher was talking something like, "There will be a floating output at the base when nothing is connected so we use the R7 (10k) for ...
3
votes
3answers
69 views

How to enable Output pin to high by default in Arduino Uno?

In Arduino Uno, I noticed that when I set a PIN to output, the default initial state is low. Is there a way to set the initial output state to high? The pinmode documentation supports only input, ...
0
votes
1answer
96 views

STM32F103 GPIO and wrong configurations

I have a few questions about gpio. First What if two push-pull pins with high level connected? My point of view is that there is no way for current and nothing bad will happen. And reading of pin ...
2
votes
1answer
89 views

Why is my pull-up resistor not working?

here's my schematic. I've got this circuit hooked up to those pins. Q1 is P-channel MOSFET (AO3401A), I've also got an ATmega328P not pictured, and POWER_BUTTON is connected to PC4 of the ...
4
votes
3answers
174 views

I2C communication won't start unless SDA pullup resistor is reinserted

I'm working on a project where a PIC12LF1552 microprocessor is using I2C to talk to a TMP75 temperature sensor. Like the title says, a very strange issue keeps happening. Overview Every time I ...
1
vote
1answer
71 views

Water Level Indicator

I have built water level indicator circuit as shown in this figure. If the inputs of IC 74148 is connected directly to negative supply through pull up resistor it works, but if it is connected to ...
1
vote
1answer
44 views

interfacing external push button to msp430 using energia

I am writing code in Energia using the mso430g2553 launchpad and an external pushbutton with a pullup resistor. The code should simply display the state of the button on the serial monitor, 1 for ...
1
vote
1answer
43 views

To make input-output pin of sensor high from mcu is it better to give logic high from mcu or making the mcu-pin input with pull-up?

I drive sht11 temperature-humidity sensor from mcu, the reference design from MikroElektronika uses the following: To make sda pin high, the pin connected to sda (which is pull-up) is not given to ...
7
votes
4answers
500 views

What small IC could give switchable I2C pullups?

My goal is to replace a DPST on pullup resistors with something simple, cheap and very small that can be activated with the I2C bus voltage. I thought that this might be a common enough requirement ...
-1
votes
1answer
82 views

Pull-up resistor causing unintentional voltage divider?

I'm trying to use the output of a comparator as the input of a schmitt trigger built with positive feedback on another comparator. Both have open collector outputs. When the two are not connected, ...
-2
votes
1answer
128 views

Pull Up/Pull Down Resistor Confusion

I have googled the crap out of this but I can never find a good answer. In a circuit with a pull up resistor, why is the input pin fed current with a resistor? A pull down resistor circuit doesn't do ...
0
votes
2answers
232 views

Should the output of logic gate have pull-up or pull-down resistor

I am a bit confused whether my chosen AND gate should have pull-up or pull-down resistor on the outputs, as I don't see any sentence containing words like pull-up/down or sink or source ... but as far ...
0
votes
1answer
347 views

stm32f4 pull up resistor value

I'am working with Stm32f4 discovery board , i need to know the right value of the pull up resistor on the GPIO port all there is on the datasheet is : week pull up Thank you
0
votes
2answers
53 views

DIP switch on Atmega32, are external pull-ups neccessary?

I'm connecting a DIP switch to an Atmega32 as shown in the diagram above. This works well in my application so far. However the common opinion seems to be that external pullups are necessary for a ...
1
vote
3answers
248 views

Why do we need a pull-up resistor if we can just make a short to the power source? [duplicate]

I saw the term pull-up resistor being mentioned everywhere, but I haven't grasp the reasoning behind its use. For example, I saw one in the book Practical Electronics for Inventors, in this schematic ...
1
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1answer
129 views

NMOS - Why is a resistor necessary?

I understand how the logic levels of an NMOS work with a pull-up resistor. 1. What would happen though if there was no resistor attached? (What would the logic levels look like and why?) 2. What ...
-1
votes
1answer
82 views

Pull Up/Down vs High/Low Pull [closed]

Is pull up the same as high pull? Is pull down the same as low pull? If they are different what is the difference? These two terms are all mentioned in this guide and it is kinda confusing.
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2answers
82 views

Pull up/ Pull down resistor

I am using an external pullup resistor on my input pin, and a switch connected to GND. It is like in the picture below. In the below picture, when the switch is open, the MCU input pin will see a ...
3
votes
1answer
67 views

Electron flow with pulling resistors

I'm very confused on the idea of pulling resistors. I get that they set the default voltage to a value so that you don't get a floating high or low value, but I don't get the application in TTL. So ...
3
votes
2answers
186 views

Temperature compensation in transistor current cource

I am working with analysis of BJT current source. I didn't get the explanation of temperature compensation in NPN transistor with PNP and pull up resistor. How does it work actually?
0
votes
1answer
94 views

Pull Up Resistor on signal too low (Tx from HC-06), why it get fixed?

I had problems with a bluetooth module HC-06 because it didnt transmit the data by UART, but someone told me to add a pullup resistor between the VCC and the TX of the module, it works, we tested with ...
3
votes
3answers
110 views

How to avoid Attiny84 being powered on by a pulled up data line?

I've developed a simple sensor board based on the Attiny84a microcontroller which is able to communicate over a serial connection. I'm using an arduino bootloader and the SoftwareSerial library on ...
1
vote
1answer
119 views

How could this transistor be in saturation?

For this RTL circuit (RTL inverter with active pull-up): The textbook says that in the output high state, Qp is in saturation and the circuit looks like: I wonder how this is possible? $$Rcp = ...
2
votes
2answers
508 views

How does strength work in Verilog?

I want to create an assignment which takes care of pull-ups from a port pin. I wrote the following: ...
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0answers
60 views

LVCMOS33 to LVCMOS25 using a diode and pull up resistor

I am trying to interface LVCMOS33 to LVCMOS25 without using a supply voltage of 2.5V. I was thinking of using a schottky diode and a pull up resistor. I am trying to do this to two signals; ...
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votes
2answers
99 views

about getting the ACK right in TWI

okay, i'm an old EE that mostly just writes DSP code and dinks around in MATLAB. but once in a while i get to dabble in more concrete things. and, actually, this TWI-bit-banging code seems to work, ...
0
votes
1answer
104 views

Voltage divider with pull up resistor

I'm trying to trigger a logic fall signal on my raspberry pin input which is set with a internal pullup resitor (on 3V). The input raw signal I have in actually a 0V which change to -5V during a ...
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0answers
223 views

What happens when you use internal+external pull-up resistor?

I was working with an Arduino One and this rotary encoder from SparkFun. Then, for no good reason, I put three pull-up resistors, one for each input pin (pin 2, 3 & 4) facing the encoder, like ...
0
votes
3answers
64 views

Can this active-high scenario be achieved without an external pull down resistor

If I understand correctly, few microcontrollers offer internal pull down resistors on their input pins but almost all allow for internal pull up resistors to be configured. Why exactly is that ? I ...
1
vote
4answers
272 views

What is the purpose of a pull-up resistor in a microcontroller?

I'm reading about the AVR microcontroller. In a chapter on I/O ports I've stumbled accross a concept that I have trouble understanding: the pull-up resistor. Here is a quote from the textbook: ...
0
votes
1answer
102 views

Tristate logic equivalent in NMOS logic

Suppose I have 3 signals generated by NMOS logic. Each of those signals has an associated enable pin that when driven high will result in the value of the signal appearing on the output (I should note ...
4
votes
1answer
98 views

Pull up resistor in NMOS logic value

For my senior high school project I decided to build a basic CPU from discrete components. I plan on using a 5V logic level and the current design calls for around 2000-3000 N-channel MOSFET ...
2
votes
3answers
606 views

Why are pull-up resistors required to be connected to the 2 lines of I2C? [duplicate]

Without pull-up resistors connected to the 2 lines of I2C, I2C communication fails. Why is there a need to have pull-up resistors for I2C? In contrast, UART and SPI do not need pull-up resistors. ...
0
votes
2answers
201 views

Does an active low pin need a pull up resistor?

I am interfacing a PIC24 microcontroller with this nRF24L01 2.4GHz transceiver. The transceiver has an active low interrupt pin that is toggled on transmit and a few other instances. Does this pin ...
0
votes
2answers
171 views

Controlling pull-up pins from external circuit

I have a circuit with an Arduino controlling a 2-channel, normal-off, opto-isolated relay board, 5V input signals, turning relay ON when the Arduino digital pin is set LOW. The relays are controlled ...
4
votes
2answers
112 views

Use GPIO for switchable Pullups of I2C

I'm designing a general purpose interface board and want to make available as many of the peripherals available and usable on an expansion header without the need for permanent (soldering) changes. ...
0
votes
2answers
127 views

does CompactRIO modules have builtin pull-up/down resistors

I have Compact RIO 9076 with 4 different modules: NI-9205 (Analog Input), NI-9264(Analog Output), NI-9402 (Bidirectional Digital I/O), NI-9403 (Bidirectional Digital I/O). I have several 3rd party ...
1
vote
1answer
1k views

FPGA floating pins, when place pull-up/down resistor on Input or Output

I've looked my FPGA datasheet and found that there is no pull-up/down resistors on it's pins(just a pull-up but that need to be enabled). So, when I power up my circuit I've for a "big" amount of time ...
0
votes
1answer
159 views

Is it possible to detect high impedance at FPGA input?

I am using a FPGA development board which have neither pull-up nor pull-down resister at the input side. VHDL code that I am developing has to detect either logic zero or logic one and to do ...
2
votes
1answer
67 views

Finding the Pull-up Resistor Value

I am designing a wireless sensor node that will be operating off of 1.8V. I am using an Atmel ATtiny861a MCU with a CC2520EMK radio and a 23A1024 External memory chip. I have a chip select pin for ...
0
votes
3answers
62 views

Low leakage current methods of initializing pin inputs at power up

Suppose I have an IC that has a standard level triggered input pin. I need this pin's state to be setup immediately at power on at a time when my MCU's GPIOs may not have established levels. What are ...
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vote
3answers
351 views

pull down resistor in PIR circuit

I have an motion sensor circuit. The circuit calls for a voltage of 2-15 dc volts. On the PIR data sheet the source pins calls for a pull down resistor of 47K at 5 volts. My question is if I use 8 ...
4
votes
2answers
152 views

How to default logic high after a voltage divider?

I have a 5V logic pin coming in that I want to cut down to 3.3V. When the 5V pin is detached, however, I want the pin to default logic high (3.3V). How can I choose R_pu appropriately? V_in = 5V ...
1
vote
1answer
52 views

Atmega 328 with DS1620 thermometer chip. Why is a pull-up resistor needed on the DQ line

I think understand the purpose of pull up resistors in general but in this particular case the DS1620 datasheet says that in the output mode it sources a current of 1ma (see footnote 5 on the last ...
0
votes
1answer
53 views

multiple mosfets controlling individual circuits sharing one pull up res?

i'd like to control several individual circuits using an array of MOSFETs and wondered if they have to have individual pull-up resistors or if they can share one connecting them to ground. Or do the ...
0
votes
1answer
575 views

PICkit3 MCLR to Vdd Pull-Up Resistor

I'll preempt this by saying that I'm a software person whose education (unfortunately) didn't even touch on the most basics of hardware or circuits. I'm attempting to program a PIC16f1709 microchip ...