最近有时间学学CPLD，很惭愧没能学好学透，但对于我预先想做的工作课题已经可以对付了。不求锦上添花，但求能解决实际问题。 我认为学习CPLD首先有必要了解一下GAL的编程，虽然他们的语言可能不同，但是基本的程序思路、结构、需要表达的方法有很多类似的 地方，马马虎虎地说：N个GAL加在一起就是CPLD,严格说是不对的，但是对于没有入门之前可以简单的这样理解。所以粗略地了解一下GAL的 编程对学习CPLD有很大帮助。我希望我能够讲清楚学习掌握一些基本编程，通过学习能够掌握手头的简单应用方法，而进一步的深入研究就 不在入门之列了，掌握的基本方法就可以按自己的想法动手试验，然后才能步步深入。 GAL编程，一般可以使用ABEL语言编程，ABEL的语法基本上是由一组逻辑表达式进行叙述，一片GAL能帮我完成什么功能呢？或者说能改 变成什么样的芯片呢？对GAL来说，由于内部的逻辑电路（门）比较少，一般只能完成一些简单的逻辑转换、简单的计数器(位数少)、锁存器 等。一般简单来讲，GAL的可用输入比输出多，如果想用他做地址译码器是比较合适的，在单片机的应用中，往往需要用几个不同的门电路组 合或加上138之类的3-8译码器组合，译出几个特定地址，这才是GAL的专长，可以在一个芯片内完成，使得你的电路简洁，而且输入输出在不 违背基本约定的前提下可以随意调换，使得布板走线容易。先看看下面的一个例子： module M273 "这是一个类似于74LS273的锁存器程序 title '8-bit Locker xiaoqi Data I/O Corp.' M273 device 'P16V8R'; "这里我们使用GAL16V8进行编程 "引脚定义，注意CLK,OE的定义只能使用芯片约定的引脚，不能转移 Clk,OC,I0,I1,I2,I3,I4,I5,I6,I7 pin 1,11,2,3,4,5,6,7,8,9; Q0,Q1,Q2,Q3,Q4,Q5,Q6,Q7 pin 19,18,17,16,15,14,13,12; H,L,X,Z,K = 1,0, .X.,.Z.,.K.; "类似于c语言的宏定义（代数） Input = [I7,I6,I5,I4,I3,I2,I1,I0]; "两个集合群定义 Output = [Q7,Q6,Q5,Q4,Q3,Q2,Q1,Q0]; equations " global [Q7..Q0].clk = Clk; "输出与CLK有关 [Q7..Q0].oe = !OC; "输出受!OC才有效 WHEN !OC THEN "如果OC为低电平则 Output := Input; "受时钟触发的锁存 test_vectors ' test Load & Output' ([Clk,OC, Input ] -> Output) "写入芯片以后编程器需要校验的内容 [ K, L, ^h55 ] -> ^h55; [ K, L, ^hAA ] -> ^hAA; [ K, L, ^hFF ] -> ^hFF; [ X, H, X ] -> Z; end M273 "本模块程序结束 当我基本上设计完这个GAL后，在一个具体的电路中使用他，由于布板走线的原因，我需要将其中输出线Q0与Q1对换，这可以将上面的引 脚定义中的Q0,Q1的表达顺序对换一下就行了，当然这样的使用并不提倡，但说明他确实能给你带来不少的灵活性。 有时候我需要两组不同的互不关联的逻辑电路，我们也可以用一个GAL完成，只要引脚和内部宏单元够用，例如下面我设计了一个LED七 段码的译码器，还有IO富裕，则我可以利用多余的IO设计一个简单的地址译码电路，下面的程序是为了使一般的七段码LED数码管显示多几个 特殊字符，使用了5条输入数据线，多余的IO我们独立的制作了一个任意逻辑电路： module BCD7 title 'LED HEX-to-seven-segment decoder Use GAL16V8. xiaoqi Jan.5.2002' " a " --- HEX-to-seven-segment decoder similar to the 7449 " f| g |b " --- 笔段定义 " e| d |c " --- bcd7 device 'P16V8R'; OI2,OI1,OI0,D0,D1,D2,D3,D4 pin 7,8,9,2,3,4,5,6; a,b,c,d,e,f,g,OOC pin 13,14,15,16,17,18,19,12 istype 'com'; bcd = [D4,D3,D2,D1,D0]; led = [a,b,c,d,e,f,g]; ON,OFF = 0,1; " 共阳结构数码管 L,H,X,Z = 0,1,.X.,.Z.; @dcset truth_table ( bcd -> [ a , b , c , d , e , f , g ]) 0 -> [ ON, ON, ON, ON, ON, ON, OFF]; "0 1 -> [OFF, ON, ON, OFF, OFF, OFF, OFF]; "1 2 -> [ ON, ON, OFF, ON, ON, OFF, ON]; "2 3 -> [ ON, ON, ON, ON, OFF, OFF, ON]; "3 4 -> [OFF, ON, ON, OFF, OFF, ON, ON]; "4 5 -> [ ON, OFF, ON, ON, OFF, ON, ON]; "5 6 -> [ ON, OFF, ON, ON, ON, ON, ON]; "6 7 -> [ ON, ON, ON, OFF, OFF, OFF, OFF]; "7 8 -> [ ON, ON, ON, ON, ON, ON, ON]; "8 9 -> [ ON, ON, ON, ON, OFF, ON, ON]; "9 10 -> [ ON, ON, ON, OFF, ON, ON, ON]; "A 11 -> [OFF, OFF, ON, ON, ON, ON, ON]; "b 12 -> [OFF, OFF, OFF, ON, ON, OFF, ON]; "c 13 -> [OFF, ON, ON, ON, ON, OFF, ON]; "d 14 -> [ ON, OFF, OFF, ON, ON, ON, ON]; "E 15 -> [ ON, OFF, OFF, OFF, ON, ON, ON]; "F 16 -> [OFF, ON, ON, OFF, ON, ON, ON]; "H 17 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 18 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 19 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 20 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 21 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 22 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 23 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 24 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 25 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 26 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 27 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 28 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 29 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 30 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 31 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; truth_table ( [OI2 , OI1, OI0] -> [ OOC ]) "多余IO制作一个门电路 [ 0, 0, 0] -> [ 1 ]; "这个逻辑关系可以随意设定 [ 1, 0, 0] -> [ 0 ]; [ 0, 1, 0] -> [ 0 ]; [ 0, 0, 1] -> [ 0 ]; [ 1, 1, 0] -> [ 0 ]; [ 1, 0, 1] -> [ 0 ]; [ 0, 1, 1] -> [ 0 ]; [ 1, 1, 1] -> [ 1 ]; "校对部分 test_vectors ( bcd -> [ a , b , c , d , e , f , g ]) 0 -> [ ON, ON, ON, ON, ON, ON, OFF]; "0 1 -> [OFF, ON, ON, OFF, OFF, OFF, OFF]; "1 2 -> [ ON, ON, OFF, ON, ON, OFF, ON]; "2 3 -> [ ON, ON, ON, ON, OFF, OFF, ON]; "3 4 -> [OFF, ON, ON, OFF, OFF, ON, ON]; "4 5 -> [ ON, OFF, ON, ON, OFF, ON, ON]; "5 6 -> [ ON, OFF, ON, ON, ON, ON, ON]; "6 7 -> [ ON, ON, ON, OFF, OFF, OFF, OFF]; "7 8 -> [ ON, ON, ON, ON, ON, ON, ON]; "8 9 -> [ ON, ON, ON, ON, OFF, ON, ON]; "9 10 -> [ ON, ON, ON, OFF, ON, ON, ON]; "A 11 -> [OFF, OFF, ON, ON, ON, ON, ON]; "b 12 -> [OFF, OFF, OFF, ON, ON, OFF, ON]; "c 13 -> [OFF, ON, ON, ON, ON, OFF, ON]; "d 14 -> [ ON, OFF, OFF, ON, ON, ON, ON]; "E 15 -> [ ON, OFF, OFF, OFF, ON, ON, ON]; "F 16 -> [OFF, ON, ON, OFF, ON, ON, ON]; "H 17 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 18 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 19 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 20 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 21 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 22 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 23 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 24 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 25 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 26 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 27 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 28 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 29 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 30 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; 31 -> [OFF, OFF, OFF, OFF, OFF, OFF, OFF]; "附加逻辑电路校对 test_vectors ( [OI2 , OI1, OI0] -> [ OOC ]) [ 0, 0, 0] -> [ 1 ]; [ 1, 0, 0] -> [ 0 ]; [ 0, 1, 0] -> [ 0 ]; [ 0, 0, 1] -> [ 0 ]; [ 1, 1, 0] -> [ 0 ]; [ 1, 0, 1] -> [ 0 ]; [ 0, 1, 1] -> [ 0 ]; [ 1, 1, 1] -> [ 1 ]; end BCD7 以上两个例程都是用abel4编译的，GAL编程并不很复杂，作为一般应用，编编这样的电路就已经可以对付一阵子了。如果想动手的可以 到主页上下载ABEL4软件。有关这个软件的安装使用方法，请阅读解压后的READ.ME。安装ABEL4以后，软件提供了一大堆的实例演示程序， 稍作修改就可以为你解决实际需要，篡改是学习入门的捷径，试试看吧。 最后推荐初学者读一读这份由"晓风"编写的PLD入门的好教材：pld.rar（中文PDF文档）
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