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2.MCS-51 pin diagram
3. Pin introduction
VCC (40 feet): Connect the +5 V power supply positive terminal.
VSS (20 feet): Connect to the +5 V power supply ground.
XTAL1 (19 feet): Connect one end of the external quartz crystal. Inside the microcontroller, it is the input to an inverting amplifier that forms the on-chip oscillator. When an external clock is used, this pin is grounded for HMOS microcontrollers; for CHMOS microcontrollers, this pin acts as an input for the external oscillator signal.
P0 port (39~32 feet): P0.0~P0.7 are collectively referred to as P0 port. It can be used as a quasi-bidirectional input/output port when the off-chip memory is not connected and the I/O port is not extended. When an off-chip memory or an expansion I/O port is connected, the P0 port is time-multiplexed into a lower 8-bit address bus and a bidirectional data bus.
P1 port (1~8 feet): P1.0~P1.7 are collectively referred to as P1 port, which can be used as quasi-bidirectional I/O port. For the 52 sub-series, P1.0 and P1.1 have a second function: P1.0 can be used as the count pulse input terminal T2 of the timer/counter 2, and P1.1 can be used as the external control of the timer/counter 2. End T2EX.
P2 port (21~28 feet): P2.0~P2.7 are collectively referred to as P2 port, generally can be used as quasi-bidirectional I/O port; connected with off-chip memory or extended I/O port and addressing range exceeding 256 In bytes, the P2 port is used as the upper 8-bit address bus.
P3 port (10~17 feet): P3.0~P3.7 are collectively referred to as P3 port. In addition to being used as a quasi-bidirectional I/O port, each bit can be used for the second function, and each pin of the P3 port can be independently defined as the input/output or the second function of the first function. The second function of the P3 port is shown in Table 2.1.