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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"><title>Procyon AVRlib: timer128.h Source File</title><link href="dox.css" rel="stylesheet" type="text/css"></head><body><!-- Generated by Doxygen 1.3.6 --><div class="qindex"><a class="qindex" href="main.html">Main Page</a> | <a class="qindex" href="modules.html">Modules</a> | <a class="qindex" href="annotated.html">Data Structures</a> | <a class="qindex" href="files.html">File List</a> | <a class="qindex" href="functions.html">Data Fields</a> | <a class="qindex" href="globals.html">Globals</a></div><h1>timer128.h</h1><a href="timer128_8h.html">Go to the documentation of this file.</a><div class="fragment"><pre>00001 <span class="comment">/*! \file timer128.h \brief System Timer function library for Mega128. */</span>00002 <span class="comment">//*****************************************************************************</span>00003 <span class="comment">//</span>00004 <span class="comment">// File Name : 'timer128.h'</span>00005 <span class="comment">// Title : System Timer function library for Mega128</span>00006 <span class="comment">// Author : Pascal Stang - Copyright (C) 2000-2003</span>00007 <span class="comment">// Created : 11/22/2000</span>00008 <span class="comment">// Revised : 02/10/2003</span>00009 <span class="comment">// Version : 1.1</span>00010 <span class="comment">// Target MCU : Atmel AVR Series</span>00011 <span class="comment">// Editor Tabs : 4</span>00012 <span class="comment">//</span>00013 <span class="comment">// This code is distributed under the GNU Public License</span>00014 <span class="comment">// which can be found at http://www.gnu.org/licenses/gpl.txt</span>00015 <span class="comment">//</span>00016 <span class="comment">//</span>00017 <span class="comment">// Notes: The Atmel AVR Series Processors each contain at least one</span>00018 <span class="comment">// hardware timer/counter. Many of the processors contain 2 or 3</span>00019 <span class="comment">// timers. Generally speaking, a timer is a hardware counter inside</span>00020 <span class="comment">// the processor which counts at a rate related to the main CPU clock</span>00021 <span class="comment">// frequency. Because the counter value increasing (counting up) at</span>00022 <span class="comment">// a precise rate, we can use it as a timer to create or measure </span>00023 <span class="comment">// precise delays, schedule events, or generate signals of a certain</span>00024 <span class="comment">// frequency or pulse-width.</span>00025 <span class="comment">// As an example, the ATmega163 processor has 3 timer/counters.</span>00026 <span class="comment">// Timer0, Timer1, and Timer2 are 8, 16, and 8 bits wide respectively.</span>00027 <span class="comment">// This means that they overflow, or roll over back to zero, at a</span>00028 <span class="comment">// count value of 256 for 8bits or 65536 for 16bits. A prescaler is</span>00029 <span class="comment">// avaiable for each timer, and the prescaler allows you to pre-divide</span>00030 <span class="comment">// the main CPU clock rate down to a slower speed before feeding it to</span>00031 <span class="comment">// the counting input of a timer. For example, if the CPU clock</span>00032 <span class="comment">// frequency is 3.69MHz, and Timer0's prescaler is set to divide-by-8,</span>00033 <span class="comment">// then Timer0 will "tic" at 3690000/8 = 461250Hz. Because Timer0 is</span>00034 <span class="comment">// an 8bit timer, it will count to 256 in just 256/461250Hz = 0.555ms.</span>00035 <span class="comment">// In fact, when it hits 255, it will overflow and start again at</span>00036 <span class="comment">// zero. In this case, Timer0 will overflow 461250/256 = 1801.76</span>00037 <span class="comment">// times per second.</span>00038 <span class="comment">// Timer0 can be used a number of ways simultaneously. First, the</span>00039 <span class="comment">// value of the timer can be read by accessing the CPU register TCNT0.</span>00040 <span class="comment">// We could, for example, figure out how long it takes to execute a</span>00041 <span class="comment">// C command by recording the value of TCNT0 before and after</span>00042 <span class="comment">// execution, then subtract (after-before) = time elapsed. Or we can</span>00043 <span class="comment">// enable the overflow interrupt which goes off every time T0</span>00044 <span class="comment">// overflows and count out longer delays (multiple overflows), or</span>00045 <span class="comment">// execute a special periodic function at every overflow.</span>00046 <span class="comment">// The other timers (Timer1 and Timer2) offer all the abilities of</span>00047 <span class="comment">// Timer0 and many more features. Both T1 and T2 can operate as</span>00048 <span class="comment">// general-purpose timers, but T1 has special hardware allowing it to</span>00049 <span class="comment">// generate PWM signals, while T2 is specially designed to help count</span>00050 <span class="comment">// out real time (like hours, minutes, seconds). See the</span>00051 <span class="comment">// Timer/Counter section of the processor datasheet for more info.</span>00052 <span class="comment">//</span>00053 <span class="comment">//*****************************************************************************</span>00054 00055 <span class="preprocessor">#ifndef TIMER128_H</span>00056 <span class="preprocessor"></span><span class="preprocessor">#define TIMER128_H</span>00057 <span class="preprocessor"></span>00058 <span class="preprocessor">#include "<a class="code" href="global_8h.html">global.h</a>"</span>00059 00060 <span class="comment">// constants/macros/typdefs</span>00061 00062 <span class="comment">// Timer/clock prescaler values and timer overflow rates</span>00063 <span class="comment">// tics = rate at which the timer counts up</span>00064 <span class="comment">// 8bitoverflow = rate at which the timer overflows 8bits (or reaches 256)</span>00065 <span class="comment">// 16bit [overflow] = rate at which the timer overflows 16bits (65536)</span>00066 <span class="comment">// </span>00067 <span class="comment">// overflows can be used to generate periodic interrupts</span>00068 <span class="comment">//</span>00069 <span class="comment">// for 8MHz crystal</span>00070 <span class="comment">// 0 = STOP (Timer not counting)</span>00071 <span class="comment">// 1 = CLOCK tics= 8MHz 8bitoverflow= 31250Hz 16bit= 122.070Hz</span>00072 <span class="comment">// 2 = CLOCK/8 tics= 1MHz 8bitoverflow= 3906.25Hz 16bit= 15.259Hz</span>00073 <span class="comment">// 3 = CLOCK/64 tics= 125kHz 8bitoverflow= 488.28Hz 16bit= 1.907Hz</span>00074 <span class="comment">// 4 = CLOCK/256 tics= 31250Hz 8bitoverflow= 122.07Hz 16bit= 0.477Hz</span>00075 <span class="comment">// 5 = CLOCK/1024 tics= 7812.5Hz 8bitoverflow= 30.52Hz 16bit= 0.119Hz</span>00076 <span class="comment">// 6 = External Clock on T(x) pin (falling edge)</span>00077 <span class="comment">// 7 = External Clock on T(x) pin (rising edge)</span>00078 00079 <span class="comment">// for 4MHz crystal</span>00080 <span class="comment">// 0 = STOP (Timer not counting)</span>00081 <span class="comment">// 1 = CLOCK tics= 4MHz 8bitoverflow= 15625Hz 16bit= 61.035Hz</span>00082 <span class="comment">// 2 = CLOCK/8 tics= 500kHz 8bitoverflow= 1953.125Hz 16bit= 7.629Hz</span>00083 <span class="comment">// 3 = CLOCK/64 tics= 62500Hz 8bitoverflow= 244.141Hz 16bit= 0.954Hz</span>00084 <span class="comment">// 4 = CLOCK/256 tics= 15625Hz 8bitoverflow= 61.035Hz 16bit= 0.238Hz</span>00085 <span class="comment">// 5 = CLOCK/1024 tics= 3906.25Hz 8bitoverflow= 15.259Hz 16bit= 0.060Hz</span>00086 <span class="comment">// 6 = External Clock on T(x) pin (falling edge)</span>00087 <span class="comment">// 7 = External Clock on T(x) pin (rising edge)</span>00088 00089 <span class="comment">// for 3.69MHz crystal</span>00090 <span class="comment">// 0 = STOP (Timer not counting)</span>00091 <span class="comment">// 1 = CLOCK tics= 3.69MHz 8bitoverflow= 14414Hz 16bit= 56.304Hz</span>00092 <span class="comment">// 2 = CLOCK/8 tics= 461250Hz 8bitoverflow= 1801.758Hz 16bit= 7.038Hz</span>?? 快捷鍵說明
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