Problems with current sinking and current sourcing of the I/O port of the msp430 microcontroller
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MSP430 IO port current source and sink problem
The digital input/output ports have the following features:
□ Each input/output bit can be programmed independently.
□ Any combination of input and output is allowed.
□ All 8 bits of P1 and P2 can be set as interrupts independently.
□ Input and output data registers can be operated independently.
□ Pull-up or pull-down resistors can be set independently.
This problem is usually discussed in digital circuits.
When the output end of the digital circuit outputs a low level, the external device will "pour" current into the output end of the digital circuit.
When the output end of the digital circuit outputs a high level, the external device will "pull out" current from the output end of the digital circuit.
When an LED is connected between the "output end of the digital circuit" and the power supply, and it lights up when the output end outputs a low level, this LED is a current sinking load.
When an LED is connected between the "output end of the digital circuit" and the ground, and emits light when the output end outputs a high level, this LED is a current-sourcing load.
Current sinking means current flowing into IC components, and current sourcing means current flowing out of IC components.
Regardless of current sinking or current sourcing, the output transistor of each IO port can limit the output current to a maximum of 6mA to ensure system safety.
Rmin=V/Imax=3.3V/6mA=550 ohms, so the 430 microcontroller is safe as long as R is greater than 550 ohms.
(1) The LED in the figure below is a current-sourcing load
Test results: The voltage drop of the light-emitting diode is about 1.7V
VR=3.3-1.7=1.6V IR=VR/R=0.31mA (so the system is safe)
(2) In the figure below, R is the current sink load.
Test results: The actual R is 5.1K, IR=VR/R=3.3V/5.1K=0.647mA (so the system is safe)
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