大哥,我刚学西门子pLc,不知道字,字节,双字起什么作用,用在哪里,看视频看昏了,能不能教我一下
推荐回答(1个)
恭喜你,你遇到了学习西门子PLC的第一个瓶颈
如果大学课程的C语言学的扎实,不会这么苦恼的
给你形象的解释一下
存手打,平时给公司的电工讲课我就这么讲
你可能听过这么一句话:计算机只认两个字“0”和“1”,也就是所谓的二进制
二进制的世界只有两个字,0和1,算加减法的时候逢2进1
啥意思?
就和10进制的逢十进一是一回事
在十进制中,1+2=3,3+4=7,那么9+1等于多少?
肯定是10,数字由一位数变成了两位数,
二进制也一样,0+1=1,这没毛病,但是1再加1呢?你可能说等于2,但是二进制的世界只有1和0,既然逢二进一,那就往前进一位,就变成了10,在二进制中10不能读十,就读一零
然后再往后加,1+1=10 10+1=11 11+1=100
啰嗦了这么多,出现的最多的一个词就是“位”
没错,二进制中的一个数字占据的位置,就是一个位
也就是你在PLC的帮助或者资料书中看到的bit
那么好玩的来了,假如我只给你一个位的空间,然后让你用这一个位向我传达信息,你能传达几个信息?
毫无疑问,只有两个信息,要么0,要么1
这就相当于按钮的“接通”和“断开”没有第三种情况
然后我和你约定好,你说0,我就明白此时按钮是断开的,你如果说1,那说明按钮接通了
那么你要想传达更多的信息怎么办?
1个位显然不够用了
现在我我给你8个位,00000000
能传达多少种信息?
256种
我们把这8个位组成的整体,又取了一个名字,叫做字节,也就是byte
那要是256种信息还不够呢?
我再给你8个位的空间,现在一共16个位了,0000000000000000
这能传达多少种信息?
65536种
然后我们再人为的给这16个位组成的整体取个名字,叫做字,也就是word
要是16个位还不够,那就再给16个,也就是32位
这就叫双字,也就是Dword,这个大写的D是啥意思?
英文单词“双份”的首字母,也就是double
位、字节、字、双字,这四个概念仅仅是表达这个数据的长度
那么还有些数据,比如整数、双整数、浮点数、BCD码,这些又是干嘛的?
举个例子,我用一个16位的字,先把最高一位摘出来
然后规定好,这一位代表正负号,当它为0的时候,它是正的,当它为1的时候,它是负的
那他就只剩下后边的15个位还能用,这就变成了多少?
-32767到0,再到正的32768
双整数只是比它又长了一半(位数长一半,不是数值乘以2)
如果看到这你都能看懂,再继续追问
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