Question: The book says that to measure the pin level of port P1, the corresponding pin needs to be set first. For example, to measure port P1.0:
ORL P1, #01H ; first set
MOV C, P1.0 ; then read the interface
Since the data given to the P1 port can generate a level, what is the point of setting it first and then measuring it? Isn't it obvious that it has become a high level? How can we measure it?
Satisfactory answer:
This is determined by the internal structure of the pin.
When the pin of the microcontroller outputs a low level, there is a strong pull-down circuit inside the pin, which can make the pin output a low level stably, and the pin can withstand a sink current of up to 20mA (different models vary);
when the pin of the microcontroller outputs a high level, the pull-up circuit inside the pin has little effect, although it can make the pin output a high level, but if the external circuit pulls the pin's potential down, it will be read back to 0 when reading.
This is the so-called "quasi-bidirectional port".
To use the pin input, you should first output 1 to put the pin in a weak pull-up input state.
Previous article：P1 external 4x4 keyboard reverse scanning
Next article：51 MCU C language: irregular matrix keyboard
- Popular Resources
- Popular amplifiers
OPA364AIDBVR
- Learn ARM development(16)There are many things to learn about ARM, and interrupts are definitely something that needs to be learned. Since the CPU introduced interrupts, it has truly entered the multi-tasking system and greatly improved work efficiency. ...
- Learn ARM development(17)Because all embedded systems use interrupts, how does my S3C44B0 interrupt the process? Then I need to understand the whole process. To understand it in depth, the best way is to write a program ...
- Learn ARM development(18)Last time, we have learned about the interrupt handling process of ARM and how to set the interrupt function. So, does it work like this? The answer is no. Because S3C44B0 has several registers that control ...
- Embedded system debugging simulation toolAfter the embedded hardware system is designed, it needs to be debugged. Whether it is hardware debugging, software debugging or program solidification, debugging simulation tools are needed. ...
- A small question that has been bothering me recently has finally been solved~~Recently, I have not been able to understand the concept of drivers very well. Sometimes I can get a feel for it by combining some USB examples written by others, but because the ARM system does not directly explain the pins like the microcontroller ...
- Learn ARM development (1)
- Learn ARM development (2)
- Learn ARM development (4)
- Learn ARM development (6)
Professor at Beihang University, dedicated to promoting microcontrollers and embedded systems for over 20 years.
- LED chemical incompatibility test to see which chemicals LEDs can be used with
- Application of ARM9 hardware coprocessor on WinCE embedded motherboard
- What are the key points for selecting rotor flowmeter?
- LM317 high power charger circuit
- A brief analysis of Embest's application and development of embedded medical devices
- Single-phase RC protection circuit
- stm32 PVD programmable voltage monitor
- Introduction and measurement of edge trigger and level trigger of 51 single chip microcomputer
- Improved design of Linux system software shell protection technology
- What to do if the ABB robot protection device stops
- Analysis of the application of several common contact parts in high-voltage connectors of new energy vehicles
- Wiring harness durability test and contact voltage drop test method
- From probes to power supplies, Tektronix is leading the way in comprehensive innovation in power electronics testing
- From probes to power supplies, Tektronix is leading the way in comprehensive innovation in power electronics testing
- Sn-doped CuO nanostructure-based ethanol gas sensor for real-time drunk driving detection in vehicles
- Design considerations for automotive battery wiring harness
- Do you know all the various motors commonly used in automotive electronics?
- What are the functions of the Internet of Vehicles? What are the uses and benefits of the Internet of Vehicles?
- Power Inverter - A critical safety system for electric vehicles
- Analysis of the information security mechanism of AUTOSAR, the automotive embedded software framework
- [Review of Arteli Development Board AT32F421] 2. Use of peripheral ERTC
- [Mil MYD-YA15XC-T Review] + Unboxing
- How to choose between different chips in TI's Sub-1GHz product line?
- CircuitPython Electronic Chain Bracelet
- "C Programming Magic Book: Based on C11 Standard"
- [Project Source Code] 3 methods to display state machine names in Modelsim simulation based on FPGA
- Temperature sensor + I2C + serial port + PC host (pyserial) example
- MSP430G2553 internal ADC principle and routine description
- Types of PCB substrates
- What is the difference between an AD schematic and a schematic library?
京公网安备 11010802033920号