Why SPI Does Not Require Pull-Up Resistors

Hello everyone, I am Remember Cheng.I previously wrote an article:Why I2C Requires Pull-Up ResistorsI2C requires pull-up resistors due to its open-drain structure, which cannot output a high level, so external pull-up resistors must be added.When using SPI, we find that pull-up resistors are not needed. This is mainly because SPI typically uses a push-pull structure, allowing both high and low levels to be output, so external pull-up resistors are unnecessary.A push-pull circuit can be constructed using two transistors or two MOSFETs.1. Transistor Push-Pull CircuitThe following is a push-pull circuit built with transistors. When Vout outputs a high level, the current flows as shown in the diagram, supplying current to the load Rload.Why SPI Does Not Require Pull-Up ResistorsWhen Vout outputs a low level, the current flows as shown in the diagram, pulling current from the load.Why SPI Does Not Require Pull-Up Resistors2. MOSFET Push-Pull CircuitA push-pull circuit constructed with one PMOS and one NMOS is shown in the diagram below (the left side is input, and the right side is output).Why SPI Does Not Require Pull-Up Resistors

  • When the input is high, the PMOS is off, the NMOS is on, and the output is low.

  • When the input is low, the PMOS is on, the NMOS is off, and the output is high.

3. Difference Between Push-Pull and Open-DrainThe low-level driving capability of a push-pull circuit is the same as that of an OC/OD gate. The high-level driving capability is stronger than that of OC/OD because the push-pull circuit is directly connected to the power supply, while OC/OD requires pull-up resistors, and the high-level output capability depends on the size of the pull-up resistor.I have summarized the differences between push-pull and open-drain for your reference.Why SPI Does Not Require Pull-Up ResistorsThat’s all for today. I hope this information is helpful to everyone. See you in the next issue.Why SPI Does Not Require Pull-Up Resistors

END

Source: Remember ChengCopyright belongs to the original author. If there is any infringement, please contact for deletion..▍Recommended ReadingReview of My Commonly Used Embedded Development ToolsSomeone used DeepSeek to write a serial port assistant, then…Chuan Zhihui has opened a branch and is hiring embedded developers with high salaries!→ Follow for more updates ←

Related posts

  1. Renesas Becomes the MCU Leader This Year, Launches New MCU Products
  2. Simultaneous Detection of Blood Glucose and Current Sensor
  3. In-Depth Explanation of UART/I2C/SPI/1-Wire Communication Interfaces
  4. Can The ESP-32 Dominate Over STM32 in IoT?
  5. Summary of Basic C++ Syntax
  6. Why High-Speed Train Seat Numbers Are A, B, C, D, F, But Not E?
  7. SPI Communication Technology: Practical Applications of MCU and FLASH
  8. Understanding 4-Wire and 7-Wire SPI Protocols
  9. Video Tutorial | How to Set Up I2C Communication Using RX Smart Configurator
  10. Why Pull-Up Resistors are Necessary for I2C

Leave a Comment