2009年9月21日 第2章_硬件结构 双语教学_黄英_《单片机原理及应用》讲义.pptVIP

Microcontroller Principle and Application Chapter 2  Hardware structure of microcontroller 2.1.1 The features of 8051 core ? 8051 : The core of MCS-51 devices The original member of the MCS-51 familiy Block Diagram of 8051 core Figure: 2.4.1 Clock circuit Fig.1 Using the On-Chip Oscillator 2.5.3 Power down mode Home Work of Chapter 2 P43 （一） （二） ? Because Ports 1, 2, 3 have fixed internal pull-ups, they are sometimes called quasi-bidirectional ports. ? Port 0, on the other hand, is considered truly bidirectional, because it floats when configured as an input （a high-impedance input）. 2.3.1 The structure of Port 0～3 2.3 Parallel Input/output ports ? To be used as an input, the port bit latch must contain a “1”, which turns off the output driver FET. ? So the pin is pulled high by the internal pull-up resisters but can be pulled low by an external source. ? Port 1, 2, 3 have internal pull-up resisters. ? After reset, “1” writes to all port latches. 2.3.5 Operation of the pin of port 0, 2, 3 2.3 Parallel Input/output ports ? Please analyze by yourself ? Similar to that of port 1 Return Chapter 2 Hardware structure of microcontroller 2.4 Clock circuit and timing What’s Timing ?  The time correlation among signals in executing instructions. What’s Clock Circuit ?  To produce timing signals for running microcontroller. 2.4 Clock circuit and timing 1. On-chip oscillator ? All MCS-51 microcontrollers have an on-chip oscillator which can be used as the clock source for CPU. 2. Using the On-Chip Oscillator ? To connect a crystal or ceramic resonator between the XTAL1 and XTAL2 pins, and capacitors to ground. 2.4.1 Clock circuit C1, C2: about 30pF Range of resonator frequency : 1.2MHz～12MHz（Range） 6MHz（often） 12MHz（high speed serial communication） 40MHz（show up） 2.4.1 Clock circuit Clock Circuit: See the Fig.2 Fig.2 Clock Circuit ? The internal clock generat