Circuit diagram:
Minimum system components:
MCU, reset circuit, crystal oscillator (clock) circuit, power supply
Pins used by the minimum system:
1. Main power pin
VCC: Power input, connected to 5V power supply, pin 40
GND: Ground wire, pin 20
2. External crystal oscillator pins (two pins) generally have no direction
XTAL1: Crystal oscillator input terminal of the on-chip circuit
XTAL2: Crystal oscillator output terminal of the on-chip circuit
The function of the capacitor is to filter out the high-frequency signal of the crystal oscillator to make the crystal oscillator work more stably.
3. Reset pin
RST: Reset pin (high level reset) T = RC
When the power is first turned on, the pin is at a high level (no less than two clock cycles), the microcontroller automatically resets, and executes the program from scratch.
1 state cycle = 2 oscillation cycles; 1 machine cycle = 6 state cycles; 1-4 machine cycles = 1 instruction cycle
Oscillation period = 1/fosc = 1/12MHZ = 0.0833us
4. Other functions
EA: memory selection pin, select internal memory when connected to 5V, select external memory when low level
The MCS-51 series MCU has a total of 128 bytes of RAM, with an address range of 00H~7FH
ROM 4K bytes, address range 0-0FFFH
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