| MCU is one of the common controllers for it’s low price, better control, a widerange of applications. generally MCU have a T0and a T1timer, some still have a T2timer. Different timer have different timing ways, also have different applications.MCU timer usually loading are integers. because the characteristics of crystal frequencyand its own resources of MCU, it is workable for the time not strict occasion. Butbecause it has long accumulation error, it does not apply to accurate control. The clockof that exist a lot of questions in accuracy and synchronicity. Therefore, it is veryimportant to analyze the characteristics of the ways of MCU timer, adopt the precisetiming method, analyze the characteristics of crystal frequency, use the reasonablecontrol algorithm for accurate clock system.Take T0as an example, way0,1have interrupte error, but way2have accuratetiming for its automatic reload function. Way3often used for increasing a counteraccording to the need when T1timer used for a serial port baud rate generator. this wayalso has interrupt error. Here to choose way2analyzed. A machine cycle of thetraditional51series microcontroller need twelve clock cycle completed. This meansthat if the crystal is12MHz, so machine cycle is1us. However,the commonly usedcommunication baud rate9600bit/s,19200bit/s use11.0592MHz crystal. A machinecycle of this frequency is12/11.0592, not a integer.It results many troubles for theprecise calculation. Usually, we use timer initial value calculation software or calculatethe timer initial value according to the formula. In most cases we take an integeraccording to the initial value rounding the most close to the theoretical value. Sincethere exist accumulative error, it is not accuracy. This paper use the TKStudio softwareto analyze the accurate timing feasibility of decimal timing initial value under11.0592MHz crystal clock modules.Crystal, due to temperature, humidity, electromagnetic interference, mechanicalvibration and impact, power supply fluctuation etc exist nominal value and the actualvalue doesn’t agree with phenomenon. Thus, after a period of time running the clockmodules will be inconsistent, and need to correct them to synchronization. Here to makefour clock modules with diverse crystal frequency(one less than nominal value, twoequal to nominal value, one more than nominal value), and make up a clock system.Utilize the easy-to-use network clock, use VB software generation PC applications to sent the rough computer time to each clock module. Then take a "standard crystal"clock module as a reference source, other modules to receive reference source’sinformation. The clock modules lock and save their time first and then modificate timeafter synchronize time received.Like this, next time receiving the reference source time,the clock modules compare its own time with reference source time, using the adaptivecontrol theory to change the initial value regularly so as to keep the clock modules"sync". |
