PIC18F更高的晶体频率

该PIC具有最大的外部晶体工作频率为20兆赫（数据表表27至7）。您可以使用外部振荡器输入高达64兆赫（EC模式），这需要一个外部振荡器模块/源（不只是一个晶体-使用内部振荡器）。更高的指令执行频率是使用内部PLL电路获得的，如数据表中所解释的。



      以下为原文

    This pic has a maximum external crystal operating frequency of 20 Mhz (datasheet TABLE 27-7). You may use an external oscillator input up to 64 MHz (in EC modes), this requires an external oscillator module/source (NOT just a crystal - that uses the internal oscillator). Higher instruction execution frequecies are obtainable using the internal PLL circuitry as explained in the datasheet.

较慢的时钟使用较少的功率。更快一点。使用您的应用程序所需的内容。一些外围设备可能需要像USB那样更高的频率，而其他外围设备不会在意低频率。



      以下为原文

    A slower clock uses less power. A faster one more. 
Use what is required by your application. Some peripherals might require higher frequency like the USB while other won't mind low frequency.

谢谢你的细节。如果我使用20 MHz的外部晶体，那么什么是最大工作频率可以通过使用PIC18F46K22的内部PLL来实现？顺便说一下，在UART通信中使用内部PLL是否像FRQ抖动或温度方差等有副作用？我之所以这么问是因为我的项目很大程度上基于X2 UART在这个芯片中的使用，波特率的任何变化都会在通信中引起干扰。



      以下为原文

   


 
Thanks for the details.
 
If i use 20 MHz external crystal then what is the max. operating freq. that can be achieved by using the internal PLL of PIC18F46K22?
 
BTW is there any side effect of using the internal PLL's like freq. jitters or temperature variance etc that can effect in the UART communication? I am asking this because my project is heavily based on the usage of the x2 UARTs in this chip and any variation in the baud rate would cause disturbance in the communication. 
 
Your help is highly appreciated.

除了更快的时钟，PLL不会对您的USAR有任何有害影响。PLL代表锁相环。它被锁定在你的水晶频率上，它可能比纯水晶的输出有一点点的抖动，但是太小以至于根本不会影响USAT。



      以下为原文

    Apart from the faster clock, the PLL will not have any detrimental affect on your USART.
PLL stands for Phase Locked Loop. It is locked to your crystal frequency.
It may have a tiny bit more jitter than the pure crystal output, but too tiny to affect a USART at all.
 

我们在PLIC18F46K22上使用20 MHz振荡器的PLL能快多快。



      以下为原文

   


How much faster we can go with PLL using 20 MHz oscillator on PIC18F46K22.

我必须找到，打开和阅读数据表才能告诉你。如果你自己做的话，你可能会学到更多。



      以下为原文

    I would have to find, open and read the datasheet to be able to tell you.
You will probably learn more if you do it yourself.
 

一点也不快。看来你想让其他人都把数据表给你看。我对这些有经验的用户的耐心感到惊讶。



      以下为原文

   
no faster at all.
It seems you want everyone else to read the datasheet to you. I'm amazed by the patience all these experienced users have had.

我们在PLIC18F46K22上使用20 MHz振荡器的PLL的速度要快得多。也许你可以使用2X PLL或4X锁相环。数据表告诉我们，如果2X PLL比40MHZIF要运行最大时钟，使用16MHz石英和4X PLL…



      以下为原文

   


How much faster we can go with PLL using 20 MHz oscillator on PIC18F46K22.


Perhaps you can use 2x PLL or 4x PLL. The Datasheet tells.
If 2x PLL than you run with 40Mhz
If you want max clock, use a 16Mhz Quartz and 4x PLL...

感谢细节。我的项目是使用20 MHz外部石英良好，但有人问我为什么我不在64 MHz的时钟速度使用PIC？我对这个问题没有任何分析的答案，因为我以前在PIC16F系列的所有项目中都使用了20 MHz的石英，现在也使用PIC18F46K22。我从来没有分析过我的项目的最小最大时钟频率范围。一个主要涉及两个设备之间的通信的项目。我的PIC18F46K22的X2 UTES。一个设备波特率只有9600，而第二个设备波特率是115200。你能告诉我如何估计上面项目的最佳时钟频率吗？我知道更高频率会增加功耗，所以它意味着最小时钟频率是需要分析计算的一个参数。



      以下为原文

   


Thanks for the details. 
 
My project is working fine using 20 MHz external quartz but i was asked by someone that why am i not using the PIC at  64 MHz clock speed? I don't have any analytical answer to this question because i had used 20 MHz quartz in all my previous projects of PIC16F series and now with PIC18F46K22 also. 
 
I had never analysed the min max clock freq. range for my projects.
A project which mainly involves communication between two devices connected on x2 UARTS of my PIC18F46K22 . One device baud rate is just 9600 while the second device baud rate is 115200.
 
Can you tell me how can i estimate about the best clock frequency for the above project? I know that higher freq. will increase the power dissipation also so it means min clock freq. is the one parameter that needs to be analytically calculated.
 
Your help would be highly appreciated.

在数据表16-5中：异步模式的波特率，该表列出了在特定时钟速度下可能的波特率（标准）和从标准速率得到的误差。它还为波特率提供波特率发生器控制寄存器的值。



      以下为原文

    Look in the datasheet TABLE 16-5: BAUD RATES FOR ASYNCHRONOUS MODES
This table lists the baud rates possible (standards) at specific clock speeds and the error from the standard rate you will get. It also gives you the values for the baud rate generator control registers for each baud rate.