单片机课件(黄英)：第2章_硬件结构_双语教学.ppt

* * * * 2.3.6 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 * 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. * 2.4.1 Clock circuit 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. * Fig.1 Using the On-Chip Oscillator 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 generator produces the sequence of states that make up the microcontroller clock signal, ALE signal, and machine cycle. * 2.4.1 Clock circuit 3. How to drive the clock with an external oscillator ? Applying to the system that includes multi-microcontrollers. To synchronize the clock signals among microcontrollers. Fig.3 External Clock Drive Circuit * 2.1 Logic structure and signal pins 2.4.2 Timing Units 4 types of timing units phase, state, machine cycle, instruction cycle Pulse and State ? P（phase） : Oscillator period S（state）: Clock cycle ? S ＝ P1 ＋ P2 * 2.4.2 Timing Units 1M = 6 S = S1 ＋ S2 ＋ S3 ＋ S4 ＋ S5 ＋ S6 = 12 P If fosc = 12 MHz then 1 T M = 1 us If fosc = 6 MHz then 1 T M = 2 us 2. Machine Cycle * 2.4.2 Timing Units The maximal timing unit. The time to execute one instruction. Expressed by the number of machine cycle. According to different instruction, one IC ca