17.4.1計(jì)數(shù)器II - 計(jì)數(shù)器II

7.6.3集成加/減計(jì)數(shù)器加/減計(jì)數(shù)器(也稱可逆計(jì)數(shù)器)：既具有加法計(jì)數(shù)功能，又具有減法計(jì)數(shù)功能。本節(jié)主要介紹：?jiǎn)螘r(shí)鐘同步十進(jìn)制加/減計(jì)數(shù)器74LS190、單時(shí)鐘同步4位二進(jìn)制加/減計(jì)數(shù)器74LS191、雙時(shí)鐘同步十進(jìn)制加/減計(jì)數(shù)器74LS192和雙時(shí)鐘同步4位二進(jìn)制加/減計(jì)數(shù)器74LS193。7.6.3.1雙時(shí)鐘加/減計(jì)數(shù)器輸入輸出CRLDCP+CP-DCBAQDQCQBQA1000000DCBADCBA011加計(jì)數(shù)011減計(jì)數(shù)0111保持邏輯功能示意圖功能表清零置數(shù)計(jì)數(shù)器狀態(tài)功能說(shuō)明078901210987清零加法計(jì)數(shù)減法計(jì)數(shù)置數(shù)7.6.3.1雙時(shí)鐘加/減計(jì)數(shù)器百進(jìn)制加/減計(jì)數(shù)器7.6.3.1雙時(shí)鐘加/減計(jì)數(shù)器7.6.3.2單時(shí)鐘加/減計(jì)數(shù)器輸入輸出LDCTU/DCPDCBAQDQCQBQD0DCBADCBA100加計(jì)數(shù)101減計(jì)數(shù)11保持功能表置數(shù)邏輯功能示意圖計(jì)數(shù)器狀態(tài)功能說(shuō)明13141501222101514加法計(jì)數(shù)減法計(jì)數(shù)置數(shù)13保持7.6.3.2單時(shí)鐘加/減計(jì)數(shù)器異步串行級(jí)聯(lián)方式7.6.3.2單時(shí)鐘加/減計(jì)數(shù)器同步并行級(jí)聯(lián)方式一7.6.3.2單時(shí)鐘加/減計(jì)數(shù)器同步并聯(lián)方式二7.6.3.2單時(shí)鐘加/減計(jì)數(shù)器7.6.4移位寄存器型計(jì)數(shù)器反饋邏輯電路DSLQSL移位寄存器型計(jì)數(shù)器結(jié)構(gòu)框圖由D觸發(fā)器構(gòu)成的4位移位寄存器型計(jì)數(shù)器:常用的移位寄存器型計(jì)數(shù)器：環(huán)形計(jì)數(shù)器，扭環(huán)形計(jì)數(shù)器。7.6.4.1環(huán)形計(jì)數(shù)器DSLQSL1.電路組成2.工作原理(a)(b)(c)(d)(e)有效時(shí)序無(wú)效時(shí)序4位環(huán)形計(jì)數(shù)器時(shí)序圖7.6.4.1環(huán)形計(jì)數(shù)器3.自啟動(dòng)設(shè)計(jì)向只有一個(gè)“1”的方向轉(zhuǎn)換7.6.4.1環(huán)形計(jì)數(shù)器7.6.4.1環(huán)形計(jì)數(shù)器3.自啟動(dòng)設(shè)計(jì)7.6.4.2扭環(huán)形計(jì)數(shù)器DSLQSL4位扭環(huán)形計(jì)數(shù)器2.工作原理有效時(shí)序無(wú)效時(shí)序7.6.4.2扭環(huán)形計(jì)數(shù)器3.自啟動(dòng)設(shè)計(jì)Q4

Q3

Q2

Q1FQ4

Q3

Q2

Q1F工作狀態(tài)00001多余狀態(tài)001011000110010110010100111101101011111011010011100110100110101100001001010“突破口”rssr修改反饋，經(jīng)過(guò)一個(gè)CP節(jié)拍進(jìn)入正常時(shí)序。7.6.4.2扭環(huán)