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

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2
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2answers
158 views

Using internal pull-ups for I2C on PIC18F

I'm working with a PIC18F46J53 and it was working quite well without any troubles. Suddenly, I found a hindrance on my path. I used RB4 and RB5 pins as I2C bus pins for communicating with an EEPROM ...
0
votes
2answers
83 views

LM339 : why output +5V

This circuit diagram below is given in my book ( written by Coughlin and Driscoll ) . simulate this circuit – Schematic created using CircuitLab Here it is said that at this condition ...
1
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2answers
89 views

Can a digital input having internal pull up resistor drive a load?

simulate this circuit – Schematic created using CircuitLab I am working on MC56F8006 DSC . On power up or reset the default state of all GPIOs is inputs with internal pullups enabled. I ...
0
votes
1answer
68 views

GPIO Pin configurations [duplicate]

I went through the data sheet of STM32F4 and found the pin configuration of GPIOs. I dont understand the difference between these configurations. • Input floating • Input pull-up • Input-pull-down • ...
0
votes
3answers
426 views

Can I do without I²C pull-up resistors?

I am trying to produce a small circuit, and I am looking to reduce the part count. I recently added an I²C EEPROM which is used once when the system boots up, along with this EEPROM I added two ...
1
vote
3answers
66 views

Do I need pull-down resistor on Enable pin cd74hc4051

Can I directly connect enable pin to ground? I am not going to use it. datasheet Also can I connect all unused pins of LM324 op-amp to ground through single resistor or what configuration does it ...
5
votes
4answers
2k views

When to use pull-down vs. pull-up resistors

After learning and experimenting with microcontrollers, the concept of pull-up- and pull-down resistors has been understood and saved to my hard drive. I now understand when and how to use them, and ...
1
vote
0answers
41 views

Internal pull up resistors in a micro-controller vs external pull ups [duplicate]

Micrcontrollers such as PIC describe their pull up resistors as weak pull up resistors, what does weak signify? When/why would I want to use external pull-up resistors on I/O pins that support ...
2
votes
2answers
108 views

How can I design this pull up without wasting current/performance?

I want to move the low side enable switch of my H-bridge onto the high side, because for safety reasons it's better to turn off the tap than plug the drain. I'm powering a 24V, 35W BLDC, so it's ...
2
votes
2answers
652 views

Internal pullup for input in PIC microcontroller

Im new in PIC world. I want to ask: Do I need external pullup resistor for switches and encoders? When I was using Atmel microcontrollers - I was just turning on internal pullup resistors in ...
0
votes
1answer
71 views

Dallas 1-wire Digital Thermo - issue with strong pullup

I have 2 Dallas/Maxim DS18b20 digital thermometers connected in parasitic-power mode. If I include a strong-pullup as shown on p.6 of the datasheet, the nearer device gives good data; the further one ...
0
votes
1answer
75 views

How to get the full Vcc output from comparator?

I am working on a circuit using a comparator for a school project, but in testing it is not acting as expected. Specifically, the output is not going all the way to the higher rail voltage attached ...
13
votes
6answers
3k views

What happens if I omit the pullup resistors on I2C lines?

Just now I realized that the I2C data and clock lines (SDA and SCL) must have pullup resistors. Well, I've built a couple of clocks using the DS1307 RTC (see datasheet) according to the schematic ...
1
vote
2answers
326 views

SPI and pullups. Is it ever used in open collector configuration

Is SPI ever wired as open collector in devices calling for the use of pullup resistors? Everything seems to point to it usually being totem pole but I wonder if there are exceptions. The only pullup ...
1
vote
1answer
189 views

How do you size pull-up/down resistors? [duplicate]

The attached photo is pulled from a Piccolo DSP reference design from TI. They use 57.6k pull-up resistors and 2.2k pull-down resistors to allow configuration of boot pins at startup. I've seen all ...
2
votes
2answers
227 views

Convert microcontroller 3.3V output to 6V

I have built an h-bridge from 4 MOSFETS (PHP21N06LT) shown below. This bridge is used for motor speed control in either direction and fast stop. I have a dev board with C8051F020 microcontroller on ...
-1
votes
1answer
60 views

Detect current on intercom

I'm trying to get an input from an intercom and apparently there is GND and another wire for the call. I'd like to know when there's voltage between the call wire and the ground. I'm thinking of ...
3
votes
5answers
194 views

How much current is used with a μC GPIO input and pullup resistor?

I'm trying to understand power budgets a bit better and I have a question regarding pullups. I have a input to a microcontroller that needs to be logic high at all times. The micro goes to sleep now ...
-1
votes
1answer
150 views

how to, best way to use a linear actuator vs gear system? [closed]

I am wondering what is the best and cheap option to use in a crane like system. a linear actuator or a gear rig system with an engine. the weight at the end could be up to 100 pounds. I was ...
0
votes
1answer
38 views

GPIO pull up to different level

I am using MSP430F235 which is supplied with 2.5V on DVCC. So, all its I/Os will be in 2.5V level. Now, I want to enable a LDO in which EN pin is tied to a different level (>2.5V is the battery supply ...
2
votes
4answers
120 views

Pull up circuit current flows?

Im trying to understand how pull up/down circuits works . Let's consider this schematic : I understand that there are two possible current flows : When the button is not pressed, the current ...
3
votes
1answer
168 views

When a pin needs to stay LOW or HIGH, is it okay to connect directly to VCC or GND?

For example, I'm using an Exar Exar SP3220EBCY-L RS-232 transceiver and the typical application loop back test shows that the EN pin is connected to GND and the SHDN pin is connected to VCC. Should I ...
1
vote
1answer
76 views

CMOS 4066 pull up resistor

I'm controlling three 4066 (Quad Bilateral Switch) with two chained 74HC595 (8-bit serial-in, serial or parallel-out shift register with output latches; 3-state) Do I need to use pull up resistor ...
2
votes
1answer
119 views

I2C Pull-ups with Multiple Power Supplies

If I have an I2C Master with multiple I2C Slaves all on separate 3V3 lines (i.e. 3v3_Master, 3V3_Slave1, 3V3_Slave2... etc.) does it matter which 3V3 line the pull-up resistors on the line connect to? ...
1
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0answers
1k views

How to assign a pull-up/down resistor in Verilog for inputs?

As a newbie in FPGA world, I realized that it is possible to set pull-up/down resistors in Verilog but I don't know how. I have written my code that works just fine but when I connect my XC3S400 to ...
1
vote
3answers
177 views

How does this MOSFET circuit work?

The following circuit from a textbook models an inverter implemented by a MOSFET switch. I understand how in the first case Vout is zero, but in the second case(the switch is open), the textbook ...
1
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4answers
482 views

i2C : pull-up resistors “design pattern”, Shielded cable and connector?

I'm designing an arduino based board which will uses I2C port a lot. I want to be able to connect several slave devices, and/or connect several mother boards together (at least 4 would be great). The ...
1
vote
1answer
223 views

Arduino serial communication RX high

I'm trying to interface with a device via async serial. Here is the power on requirement from the device datasheet: Power-On Reset Requirements When applying power to the DNT900, the /RESET Pin ...
0
votes
1answer
162 views

LM311 Pull Up Resistor

If I use an LM311 Comparator, then we are required to connect a pull up resistor at the output. Does the square wave output depends on the value of the voltage the resistor pulls up to? Would it be ...
1
vote
2answers
156 views

Why is pull-up resistor disabled in OUTPUT mode

I noticed in a lot of micro datasheets that the internal pull-up resistor is disabled automatically when the GPIO is in OUTPUT mode, but I'm not sure I understand why. Is a pull up resistor never ...
1
vote
1answer
94 views

pin is pulled up to something

I was reading 17xx series` data sheet, and I had trouble understanding a specific explanation given for a major number of pins: 5 V tolerant pad providing digital I/O with TTL levels and ...
4
votes
2answers
333 views

How should I alter my PISO shift register circuit so that it works with 3.3v instead of 5v?

I've followed this Arduino guide to build a circuit using a CD4021BE PISO shift register, and 10k pulldown resistors. It works perfectly fine with the Arduino's 5v supply. I then attempted to use ...
1
vote
2answers
169 views

Basic misunderstanding about dropping down voltage going in a TTL IC using resistors

I'm having serious problems figuring this out. Below is a part of an 8-bit computer schematic. The 62256-70 is a static ram chip. I understand these 8K2 resistors are there to provide a default value ...
3
votes
3answers
171 views

Is it common for internal pull-up resistors to fail? or what would cause them to become intermittent?

I have a board based on an ASIC ARM Cortex-M3 that after months of work suddenly started to report spurious button presses. The ASIC is not our design, but a reputable company's. The buttons ...
8
votes
1answer
263 views

Pull Up and Pull Down Resistor Values [duplicate]

I usually use 10K Ohm resistors for pulling up or pulling down micro-controller lines. This is only because I have tons of them. Recently while looking up pick and place surface mount information I ...
1
vote
1answer
503 views

ATTiny45 Quadrature Decoder Pull-Up resistors

I am trying to use the ATTiny Quadrature Decoder from here. The schematic that I have attached here has two external 10K Pull-up resistors. I have looked into the ATTiny45 datasheet and it seems that ...
4
votes
2answers
384 views

How to deal with multiple pull-up resistors on modules

I was thinking about doing a modules for a development board I did a few days ago that will include spi/i2c interfaces. The problem is that I didn't included pull-up resistors in the MCU pins in the ...
1
vote
2answers
148 views

How and why is “floating input” a valid state for RF/IR encoder IC's?

RF/IF encoder/decoder IC's such as this one, will accept the address-pin in one of 3 states: Floating High Low As per this excellent answer, I believe "Floating" input can assume either High or ...
3
votes
2answers
2k views

I2C pull-up resistors calculation & where to place them

I'm connecting a PIC18F46K22 (master) to a PIC18F4620 (slave) using I2C. The wire between the devices is ~30cm. I'm using 400kHz without slew rate control. Later on, I'll add another 18F4620 on ~5cm ...
7
votes
5answers
625 views

Connecting push button to a controller pin

This problem is decades old but I do not see a direct answer to it on this site. I want the following: This circuit just allows to check the state of the button from inside the micro-controller. ...
5
votes
2answers
176 views

i2c external pullup kills communication

I am using an MCP23017 (which shouldn't matter tho) to extend the number of GPIO pins of an arm based linux computer using i2c-dev bitbanging. It all works fine with wires of a few centimetres. The ...
5
votes
1answer
269 views

i2c on different logic level devices

I'm having a problem making LPC2148 work with SRF10 sensor. LPC is 3.3v device with 5v compatible i2c (at least user docu claims that). On the other side there is SRF10 device which is 5v. I have ...
9
votes
1answer
337 views

Weak internal pullups on microcontrollers and EMI susceptibility

What disadvantages can I run into when using weak internal pullups (100k) on microcontrollers? I'm wondering how susceptible lines (with only parasitic trace/component capacitance) become to EMI ...
7
votes
5answers
5k views

Pull-up and Pull-down Resistor Usage on Input or Output MCU Pins

Are pull-up/down resistors (whether internal or external) only needed for MCU INPUT pins? In contrast, an MCU pin configured as an OUTPUT "knows what level it's at" because it does the driving - a ...
5
votes
3answers
427 views

DS1307-breakout-board

I want to build an RTC clock for the Raspberry Pi. Adafruit has a guide to accomplish this with Dallas DS1307. On the schematic they put a 2.2K resistor between VCC and SCL and do the same for VCC and ...
7
votes
2answers
2k views

I2C pullup resistor calculations

I am trying to drive this I2C LCD display with an ATxmega16A4U microcontroller. Both devices are listed to work with I2C clock frequencies up to 400 kHz. The two devices are the only devices on the ...
23
votes
2answers
827 views

Heuristic explanation of the usage of a pull-up (or pull-down) resistor needed

First, I acknowledge that there are several questions regarding this topic in the forum, however, the answers assume too much background knowledge of electronics to be of use to a true beginner (like ...
1
vote
1answer
290 views

i2c problem on LPC2148

I have problem with getting my LPC2148 to work with i2c devices. LPC is on 3.3v bus and i2c devices are on 5v bus with pull-up of 3k6 ohm on either 3.3v or 5v (jumper selection). What im experiencing ...
10
votes
2answers
600 views

Must IO pins each have their own pull-up/down resistor?

A very basic question: Must each IO pin of a microcontroller that is serving as an input from a switch or jumper have its own pull-up/down resistor? In this example, each pin is pulled down by a ...
1
vote
3answers
308 views

I2C - Where's the ACK

I'm working on I2C master driver for interfacing a particular peripheral. The problem I have, is that when the 9th clock arrives, the slave device doesn't pull down the SDA line. I checked the ...