Computing System

This is a C# implementation of the book The Elements of Computing Systems by Noam Nisan & Shimon Schocken. Instead of grabbing a soldering iron, all the logic is done with C# implementations of logical gates to simulate it as much as possible.

Run

Start the .NET core console application in project CS.Architecture.App.

Contents

Below is a list with the current contents of the project.

Hardware (chips)

Gates

1. Nand
2. Not
3. And
4. Or
5. Xor
6. And3
7. And16
8. Not16
9. Or16
10. Or8Way

Multiplexers

1. Mux
2. Mux16
3. Mux4Way16
4. Mux8Way16
5. DMux
6. DMux16
7. DMux4Way16
8. DMux8Way16

Arithmetic

1. HalfAdder
2. FullAdder
3. Adder16
4. Inc16
5. ALU

Sequential

1. Clock
2. DFF
3. Bit
4. Register
5. RAM8
6. RAM64
7. RAM512
8. RAM4K
9. RAM16K
10. PC (16-bit counter)

Architecture

WIP

1. CPU
2. ROM32K
3. Screen
4. Keyboard
5. Memory
6. Computer

Machine Language

A-instruction

Instruction @value causes the computer to store the specified value in the A register.

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x

Bit 15 indicates the A-instruction. x represents the value.

Used for:

• Constants
• Memory manipulation
• Jump instructions

C-instruction

Instruction dest=comp;jump causes the computer to execute a computation.

• if dest is empty, the = is omitted.
• if jump is empty, the ; is omitted.

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
1	1	1	a	c1	c2	c3	c4	c5	c6	d1	d2	d3	j1	j2	j3

Bit 15 indicates the C-instruction. Bit 14 & 13 are not used and left at 1.

Compute

Computed function is specified by the a-bit and six c-bits.

comp (a=0)	c1	c2	c3	c4	c5	c6	comp(a=1)
0	1	0	1	0	1	0
1	1	1	1	1	1	1
-1	1	1	1	0	1	0
D	0	0	1	1	0	0
A	1	1	0	0	0	0	M
!D	0	0	1	1	0	1
!A	1	1	0	0	0	1	!M
-D	0	0	1	1	1	1
-A	1	1	0	0	1	1	-M
D+1	0	1	1	1	1	1
A+1	1	1	0	1	1	1	M+1
D-1	0	0	1	1	1	0
A-1	1	1	0	0	1	0	M-1
D+A	0	0	0	0	1	0	D+M
D-A	0	1	0	0	1	1	D-M
A-D	0	0	0	1	1	1	M-D
D&A	0	0	0	0	0	0	D&M
D|A	0	1	0	1	0	1	D|M

Destination

Stores the computed value.

• d1 in the A register
• d2 in the D register
• d3 in memory

d1	d2	d3	Mnemonic	Destination
0	0	0	null	Value is not stored
0	0	1	M	Memory[A] (memory register addressed by A)
0	1	0	D	D register
0	1	1	MD	Memory[A] and D register
1	0	0	A	A register
1	0	1	AM	A register and Memory[A]
1	1	0	AD	A register and D register
1	1	1	AMD	A register, Memory[A], and D register

Jump

Change the PC to jump to another instruction.

j1 (out < 0)	j2 (out = 0)	j3 (out > 0)	Mnemonic	Effect
0	0	0	null	No jump
0	0	1	JGT	If out > 0 jump
0	1	0	JEQ	If out = 0 jump
0	1	1	JGE	If out >= 0 jump
1	0	0	JLT	If out < 0 jump
1	0	1	JNE	If out != 0 jump
1	1	0	JLE	If out <= jump
1	1	1	JMP	Jump

Assembler

TBA

High-Level Language

TBA

Operating System

TBA