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Questions tagged [pullup]

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
57 views

MCP25625 SPI MISO Not Responding

As per title, I'm trying to send a simple 'READ' (0x03) command to the device and get the contents of the CANCTRL register (0x0F). I even moved past our project board and bought Microchip's ...
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3answers
90 views

Fail safe led circuit

My question is about how to turn on a led before the GPIO pin has been initiated. When the IC has just been powered on and has not yet been initiated the GPIO pins remains in state HI-Z. In Circuit-1 ...
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2answers
42 views

Why is the 1-wire pull-up resistor not integral?

I've read that the 1-wire pullup resistor is included so that either the master or the slave device can pull the line low in order to communicate. Makes perfect sense: if the device had a transistor ...
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1answer
54 views

The MOSI pin of SPI1 on STM32L073 is not giving output without pull-up resistor

I am working on SPI communication with STM32L073. I download the example program of ST to MCU but SPI1 did not work. So I looked at the SCK pin of MCU with oscilloscope and it works fine. But when I ...
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6answers
5k views

Is a pull up/down resistor really necessary?

Logical reading (1 or 0) of a micro-controller input GPIO pin may float if it is neither connected to VCC nor GND; someone said it is because of surrounding RF interference. When a floating GPIO ...
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1answer
688 views

pull-ups between logic gates

I'm trying to understand why, on this circuit bit, they used pull-ups resistors between logic ICs of the 74LS and CD4000 families. Specifically I'm talking about resistor array RM1 and R1. All the ICs ...
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1answer
34 views

AVR ATtiny1634 - PB3 as Input and Watchdog Timer

I'm quite a beginner in AVRs and this is my first project soldering the microcontroller and programming it on board. I know the ATtiny1634 QFN might not me the best micro for a beginner, but ...
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1answer
147 views

Weird behavior on a pull-down resistor in my design

I am using a 74LS173 D Flip Flop that has some control lines that may be floating at times before they are asserted. To avoid the control line from doing something I don’t want it to do doing this ...
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0answers
43 views

Switchable Pullup (Automotive)

We are looking to add to a product software-controllable pullups on sensor signal lines. Currently the signal lines we hardwire to a pullup of 5V via a 2K7 resistor, but other systems allow software-...
0
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1answer
52 views

I2C pull-up to multiple voltage question

Quick rundown of what's going on: I am using two PIC32MX to both be masters of I2C. They will be remotely controlled to determine who is the master at any given moment. Due to redundancy purposes, ...
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1answer
48 views

3.3V I2C Logic on 1.8V Device

I have designed a board with the ICM-20789, but am having trouble keeping stable voltage values on the I2C bus. Datasheet I have followed the schematic that was listed inside the datasheet, and that ...
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1answer
69 views

Micron NOR unused pins have pull-ups. Any danger just leaving them there?

I have a board designed for a dual-die Micron MT25QL512 QSPI NOR flash. These parts are in short supply, but the board fabricator had some single-die MT25QL128, and used them instead. The single-die ...
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1answer
25 views

Are external pullup resistors required D I/O pins on RN4870/71?

Are external pull-up resistors required on RN4870/71 for pins like "P1_1"? The datasheet mentions D I/O pins being "pulled-high", is it pulled high with internal resistors or programmatically from the ...
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0answers
50 views

Reading high voltage output NPN proximity sensor with Ardunio YUN

I have a NPN proximity sensor with rating voltage 6-36 VDC. (https://www.amazon.co.uk/gp/product/B07SD9VYDH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) To power it up, I use a 24 VDC power ...
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1answer
66 views

Pull-up resistor in parallel with Schottky barrier diode

I was looking at the Zynq-7000 SOC startup sequence designed in the Zynq Evaluation and Development board (ZedBoard), which requires specific voltage level regulation sequence (1.0V, 1.8V, 3.3V and 1....
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0answers
62 views

Using internal pullup, pulldown resistors to find floating IOs

I want to find at runtime if a GPIO is floating (nothing connected to it). I assumed I'd find tons of answers on Google, but maybe I'm searching wrong. My approach has been to: enable the internal ...
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1answer
60 views

pull-up resistor relay (low trigger)

I'm having issues controlling a single relay module with an arduino. It works fine when its up and running but the relay initially starts triggered until the arduino can send a "high" signal to turn ...
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4answers
360 views

Why would you enable pullup for a GPIO pin in push-pull mode?

In this STM32L486xx HAL User Manual (note: 36 MB!) is an example for GPIO configuration to power an external LED on page 53. The code lines that are confusing me are these two: ...
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1answer
45 views

Connecting logic gate input pin with pull up resistor to another driver input pin doesn't keep the voltage

I have a circuit with logic gates that implements a function in order to get 3 logic control signals. This logic works with 12V or 0V for high and low states. Logic input pins will be connected to ...
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1answer
47 views

Turning a high impedance output state to a concrete voltage value using a pull up resistor

I have this switch datasheet. I also have a connector with default pins arriving to switch D point. S points are connected to another circuit point. Note: D side connector is an output connector ...
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1answer
199 views

How to correctly set logical high level on a PS/2 port?

I'm trying to make a keyboard emulator on ATmega16A. I'm currently implementing logical low as output-zero, and, since the host(?) is supposed to pull up the line, I send logical high state as input ...
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1answer
99 views

Modification to Arduino 12V Detection Circuit

I'm upgrading the interior lights on an older model vehicle. The plan is to tap into the very simple lighting circuit (always hot with a switch for on-off-door) to detect each scenario. Light switch ...
0
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1answer
42 views

Unused pins on H6 Allwinner SoC

I am looking at a reference design for the allwinner H6 SoC. My question is pretty straightforward. Why does pin B3 need to be powered if the EPHY pins are unused. Additionally, pin B4 is being pulled ...
1
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1answer
394 views

How to calculate current limiter resistors for ULN2803 and Relay?

I'm designing a digital I/O, and for the outputs I have ULN2803 and relays. I have the schematic below. The coil current of relay is 16.7mA, ULN2803's max input current is 1.35mA and output current ...
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2answers
57 views

I2C multiple masters, one master has internal pull up, do I need external pull up?

I use 2 MCUs as 2 I2C Masters connect with 1 Slave F-Ram to Read/Write data frequency. One MCU has internal 12k Ohm pull up resistors on SDA & SCL. So do I need external pull up resistors?
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2answers
42 views

Common resistor for pulling up unused pins of ATmega2560

I am designing a PCB with ATmega2560 MCU. I have 50 unused pins in my design. I was wondering if I can pull up these 50 pins using 5 resistors such that 10 pins have a common pull up resistor. Is that ...
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1answer
768 views

Why would a USB-C adapter have a pull-up resistor?

I'm talking about a USB type-C male to USB type-A female adapter, the ones you need to connect a USB flash drive to the latest MacBooks. According to USB-C specification, this sort of adapter needs a ...
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2answers
126 views

Problem with the reset circuit for a MCU

I need help by understanding the problem with an existing MCU circuit concerning the Reset PIN (STM32 Cortex M0+: STM32L071K8): It seems something in the circuit is wrong, since it works only when I ...
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3answers
20 views

On SN65HVD1780 are external pullup and pulldowns

On transceiver SN65HVD1780 are external pullup and pulldowns required on A,B,DE,RE,D,R lines? The datasheet mentions that the part has internal pullups and pulldowns but it's not clear if external ...
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1answer
82 views

Enabling/disabling a pull-up with a microcontroller (and a level shifter)

(Split up from this question) I'm trying to interface an Arduino with an eMMC chip to bit-bang it. eMMC uses bidirectional lines, and one of them (CMD) is first used in open-drain mode (for ...
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2answers
59 views

Reset switch pullup resistor placement

I noticed that pullup resistors for reset pins that are pulled to ground with a switch are commonly placed between the power rail and the pin, for example the EN pin on an ESP32. Could the resistor ...
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2answers
85 views

Why is open collector output is called high impedance and what determines the upper limit of the pull-up resistor?

Is calling open collector output as high impedance due to the value of pull up resistor or due to the fact that the IC itself do not source any current? And what determines the upper limit value of ...
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1answer
57 views

Pullup resistor operation between the ESP32 and a Bus MCU

I have an ESP32 as my main controller and a Bus. The bus operates where Pins 55 & 56 needs to be HIGH in order for the bus to be OFF. My ESP will drive the bus by enabling it by pulling those ...
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2answers
390 views

How to connect multiple devices to UART bus? [closed]

I want to use a UART bus (RX-TX-GND) to communicate between one master and multiple slaves. NUCLEO-F401RE board is the bus master. B-L072Z-LRWAN1 and ESP32 are the slaves. Communication over UART ...
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2answers
55 views

Sensor 3.3 V to 5 V pull up schematic

I am designing a circuit for a PCB that will incorporate an ultra-sound sensor (HCSR04.) The sensor needs 5V for supply and its input pin also requires 5 V. The MCU that I am using has pins that ...
2
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1answer
140 views

Some LTspice questions. Decoupling capacitor doesn't effectively block DC. Pull up resistor voltage doesn't drop to logic low level

I'm trying to design an interfacing board that is used between a micro-controller and a phone simulator (a picture of the schematics is attached). The 44VDC is used for the phone simulator to detect ...
0
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1answer
37 views

Is Pull-up present by default?

I'm using the MC9S12DP512, Motorola's microcontroller. I was executing a service and ,at the end, I put low logic level at the pins PS4, PS5 and PS6, then after that, I configured these pins as inputs....
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1answer
79 views

IR2110 - Open Collector Output Problem

I'm trying to design an inverter and I'm using 2 IR2110 as gate drivers but my MCU board PWM outputs are open collector, I've added a pull-up and transistor to feed IR2110 with 5V pulses but it's not ...
1
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1answer
83 views

Disadvantage of using low resistor value for pull up (Strong pull up)

I was trying to choose a resistor value for a pull-up resistor I will use in my project. The project will have I2C communication and SMBus communication. When I was searching on the internet, I have ...
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1answer
138 views

How MCU pin reads whether it is being pulled up or pulled down?

I am a beginner in electronics. I searched on the web about Pull up and Pull down concepts. As far as I know, 1) When an MCU pin is pulled up, a small amount of current pass through the pull-up ...
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2answers
354 views

SMBus pull-up resistor value

Hello I need to communicate with a device using SMBus. However, I could not choose correct value for pull up resistors. Vdd is 4.9V and I use SMBus. In same conditions for I2C communications I used 2k ...
0
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1answer
35 views

How to properly use a shut pin in audio connector to prevent floating pins when disconnected

I'd like to use this RCA jack in a project that detects roughly the volume level on an RCA audio source. The circuit filters out the DC line voltage, amplifies it with a PNP transistor and then shifts ...
6
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5answers
2k views

Reasons for having MCU pin-states default to pull-up/down out of reset

On many MCUs, pin-states default to tri-stated (a.k.a. analog inputs) when the MCU resets so as to not affect the circuits they are connected to until software configures the pins. The tri-stated ...
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3answers
209 views

doubt when Arduino connects to multiple i2c devices

I am using Arduino nano to drive multiple i2c devices, actually, they are premade modules which are available on eBay. ads1115 ADC, ds3231 RTC, 20x4 character LCD i2c module, at24c02 EEPROM module ...
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2answers
146 views

Where to connect unused 555 timer ICs pins?

simulate this circuit – Schematic created using CircuitLab This question might not have a close answer since I think it heavily depends on the considered pin and IC. However, consider, for the ...
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2answers
246 views

UART/I2C Pull up resistors

I have question regarding the pull-up resistors when UART/I2C lines are running on 2.5V and GND. Is it OK if pull up resistors are used on these lines which are connected to 3.3V or Vice versa when ...
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0answers
38 views

Pull up high voltage

High voltage switching using N-FET This is my former question. The question comes down to, how should I build a pull up for a 50V operated system using 3.3V singal. The voltage I have available is ...
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1answer
80 views

Prevent design to power up when updating firmware in flash memory

I have an FPGA based design using the MachXO2 by Lattice. I wanted a quick, easy and clean way to perform firmware updates, which are frequent, so I decided to use an external flash memory (AT25SF041 ...
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2answers
51 views

Pcf8574ap to to manage the 4 address pins of 4067 multiplexer?

I have a question. I have a 4067 multiplexer connected to my Raspberry Pi, 4 GPIOs turned on or off, control the channel of the multiplexer. My problem is that if no channel is changed, my code is ...
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0answers
48 views

Opto-coupler and switching digital pins

I'm a total noob when it comes to the use of opto-couplers, but I'm trying to connect up a couple of digital pins between an ESP32 and a small voice module. There are two pins that I need to switch ...