數(shù)字秒表電路設(shè)計(jì)
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二、設(shè)計(jì)依據(jù)
本電路主要采用了二輸入與非門74LS00，十進(jìn)制BCD碼計(jì)數(shù)器74LS160，BCD七段譯碼器/驅(qū)動(dòng)器7447，555時(shí)基集成電路，七段數(shù)碼管。
利用74LS00可以組成RS觸發(fā)器，單穩(wěn)態(tài)觸發(fā)器。其74LS00的邏輯功能是有0出1，無(wú)0出0。
其邏輯表達(dá)式：Ｙ＝/（AB） ，真值表如下：
| A | B | Y |
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
十進(jìn)制BCD碼計(jì)數(shù)器74LS160具備計(jì)數(shù)分頻功能，其真值表如下：
輸入 | 輸出 | |||||||||||
CLK | CLR | LOAD | EP | ET | A | B | C | D | QA | QB | QC | QD |
X | 0 | X | X | X | X | X | X | X | 0 | 0 | 0 | 0 |
↑ | 1 | 0 | X | X | A | B | C | D | A | B | C | D |
X | 1 | 1 | 0 | X | X | X | X | X | 保持 | |||
X | 1 | 1 | X | 0 | X | X | X | X | 保持 | |||
↑ | 1 | 1 | 1 | 1 | X | X | X | X | 加法計(jì)數(shù) | |||
↑ | 1 | 0 | X | X | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
邏輯功能：當(dāng)CLR，LOAD，EP，ET均接高電平時(shí)，時(shí)鐘CP端每來(lái)一個(gè)上升沿，計(jì)數(shù)器在原來(lái)的基數(shù)上加1，并從QA，QB，QC，QD，輸出相應(yīng)的十進(jìn)制BCD碼。利用74LS160的這個(gè)功能特點(diǎn)可以設(shè)計(jì)出十分頻器，計(jì)數(shù)器。
7447為BCD七段譯碼器/驅(qū)動(dòng)器，真值表如下：
十進(jìn)制 | LT | RB | D | C | B | A | BI/RBO | a | b | c | d | e | f | g |
0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
1 | 1 | X | 0 | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 1 |
2 | 1 | X | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
3 | 1 | X | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 0 |
4 | 1 | X | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 |
5 | 1 | X | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 0 |
6 | 1 | X | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
7 | 1 | X | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
8 | 1 | X | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
9 | 1 | X | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 0 |
7447為四線-七段譯碼器，可以用來(lái)驅(qū)動(dòng)七段共陽(yáng)極數(shù)碼管，當(dāng)LT，RBI，BI，端接高電平時(shí)，從DCBA端輸入BCD碼時(shí)，從abcdefg端輸出相應(yīng)的數(shù)碼管顯示碼。
共陽(yáng)七段數(shù)碼管真值表
A | B | C | D | E | F | G | 顯示字符 |
0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
0 | 0 | 1 | 0 | 0 | 1 | 0 | 2 |
0 | 0 | 0 | 0 | 1 | 1 | 0 | 3 |
1 | 0 | 0 | 1 | 1 | 0 | 0 | 4 |
0 | 1 | 0 | 0 | 1 | 0 | 0 | 5 |
1 | 1 | 0 | 0 | 0 | 0 | 0 | 6 |
0 | 1 | 1 | 1 | 1 | 1 | 7 | |
0 | 0 | 0 | 0 | 0 | 0 | 0 | 8 |
0 | 0 | 0 | 1 | 1 | 0 | 0 | 9 |
結(jié)合四線-七段譯碼器7447可以現(xiàn)實(shí)0到9個(gè)數(shù)字。
分頻器相關(guān)文章:分頻器原理 脈沖點(diǎn)火器相關(guān)文章:脈沖點(diǎn)火器原理
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