cours/digital logic sim computer.md

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ALU binary operators

bin	operator
000	COMParison
001	zero
010	OR
011	AND
100	ADD (+)
101	SUB (-)
110	COPY A
111	COPY B

How to operate

op exec

op exec is the component that gathers the ALU and the data registers. It can :

• perform operations with the ALU
• read data : register to ALU inputs
• write data : ALU output to registers
• take input : 8 bit bus to ALU inputs
• give output : ALU output or registers to 8 bit bus

[!info] Writing data to a register It is not possible to write data directly from the 8 bit bus to the registers. If you want to register some data, you have to do the following :

• write the data to the ALU inputs (input A for example)
• set the ALU operation to copy (copy A in our example, that is 110)
• write from the alu to the register (give the register address in the 8 bit bus, and set the from ALU and to register bits)

Binary code

The binary code of the CPU. They are stored in 2 octets.

binary code	action
0000 0000 0000 0000	NOOP
SET ALU OPERATIONS
XXX0 0000 0000 0001	set X as ALU op
0000 0000 0000 0001	COMParison
0001 0000 0000 0001	ZERO
0010 0000 0000 0001	OR
0011 0000 0000 0001	AND
0100 0000 0000 0001	A+B
0101 0000 0000 0001	A-B
0110 0000 0000 0001	BYPASS A
0111 0000 0000 0001	BYPASS B
READ / WRITE
XXXX XXXX 0000 0010	X --> ALU A
XXXX XXXX 0000 0011	X --> ALU B
XXXX XXXX 0000 0110	reg X --> ALU A
XXXX XXXX 0000 0111	reg X --> ALU B
0000 0000 0000 1000	ALU --> reg

!digital logic sim computer 2023-07-18 09.57.52.excalidraw

bin	operator
000	COMParison
001	zero
010	OR
011	AND
100	ADD (+)
101	SUB (-)
110	COPY A
111	COPY B

write 10 to A -> 0001010 00000100 write 11 to B -> 0001011 00001000 write 100 to op 00000100 00010000