8bitcpu

a simple 8bit cpu with logic-circuit

加法/减法电路

A	B	S	C
0	0	0	0
0	1	1	0
1	0	1	0
1	1	0	1

$$ \begin{aligned} S= & \overline{A}B + A\overline{B} \\ C = & AB \end{aligned} $$

取反

I	C	O
0	1	1
0	0	0
1	0	1
1	1	0

$$ \begin{aligned} O =&I\overline{C} + \overline{I}C \\ \end{aligned} $$

按位取反

8
00001000

-8 
11110111 反码
11111000 补码

减法输出真值表

C0	Cn	O
0	0	0
0	1	1
1	0	0
1	1	0

$$ \begin{aligned} O = \overline{C0}Cn \end{aligned} $$

R-S触发器真值表

R	S	Q	Q'
0	0	Q	Q'
0	1	1	0
1	0	0	1
1	1	0	0

D触发器真值表

En	S	Q
0	0	0
0	1	0
1	0	0
1	1	1

D边沿触发器真值表

En	S	Q
0	0	0
0	1	0
1	1	1
1	0	1

set data then open En -> On
reset data then reset En then open En -> Off

三八译码器真值表【3位输入8位输出】

A2	A1	A0	7	6	5	4	3	2	1	0
0	0	0								1
0	0	1							1
0	1	0						1
0	1	1					1
1	0	0				1
1	0	1			1
1	1	0		1
1	1	1	1

$$ \begin{aligned} O_0 = \overline{A_2}\overline{A_1}\overline{A_0} \\ O_1 = \overline{A_2}\overline{A_1}A_0 \\ O_2 = \overline{A_2}A_1\overline{A_0} \\ O_3 = \overline{A_2}A_1A_0 \\ O_4 = A_2\overline{A_1}\overline{A_0} \\ O_5 = A_2\overline{A_1}A_0 \\ O_6 = A_2A_1\overline{A_0} \\ O_7 = A_2A_1A_0 \\ \end{aligned} $$