514 Tiny Eater 8 Bit :: Quicker, easier and cheaper to make your own chip!

How it works

This is Ben Eater's 8 Bit computer on an ASIC!

All credit for the design, amazing instructional videos, and diagams below goes to Ben Eater.

overview-with-chip-descriptions1

High level overview

Full Computer Schematic: high_level_diagram

Simple Control Signal Diagram: simple_diagram

*Note: The output register and logic to display the digits is not included on the ASIC. The 8 bit output value is put on the bus and the "output register in" control signal (oi) is on an output pin. This way you can use the data bus as a general purpose interface to any display you want. (i.e. you can read in the data to the RP2040 and show it on the screen, you can build the actual output register as shown in the videos and connect it to the PMOD header, etc.)

ASIC 2D: asic

ASIC 3D: asic_3d

How to test

To program the computer follow these steps:

enable my design in TT
send prog_mode bit high
set the four prog_address bits to the address you want to write to, put the data you want to store at that address on the I/O lines, and then pulse the clock.
since this computer only has a 4 bit address space you can only store 16 bytes total in the internal RAM.
see https://eater.net/8bit/ for more details.

Instructions

OPC	DEC	HEX	DESCRIPTION
NOP	00	0000
LDA	01	0001	Load contents of memory address aaaa into register A.
ADD	02	0010	Put content of memory address aaaa into register B, add A + B, store result in A.
SUB	03	0011	Put content of memory address aaaa into register B, subtract A - B, store result in register A.
STA	04	0100	Store contents of register A at memory address aaaa.
LDI	05	0101	Load 4 bit immediate value in register A (loads 'vvvv' in A).
JMP	06	0110	Unconditional jump. Set program counter (PC) to aaaa, resume execution from that memory address.
JC	07	0111	Jump if carry. Set PC to aaaa when carry flag is set and resume from there. When carry flag is not set, resume normally.
JZ	08	1000	Jump if zero. As above, but when zero flag is set.
	09	1001
	10	1010
	11	1011
	12	1100
	13	1101
OUT	14	1110	Output register A to 7 segment LED display as decimal.
HLT	15	1111	Halt execution.

External hardware

You will need the RP2040 or a similar microcontroller to write the program into the internal memory. If you really wanted to, you could go old school and use DIP switches and a manual clock pulse as well.

You will want to make the output register on a breadboard to connect it to the 8 bit I/O lines from the PMOD header. See https://eater.net/8bit/output for detailed design info.

#	Input	Output	Bidirectional
0	prog_mode	output_enable	data0
1	addr0		data1
2	addr1		data2
3	addr2		data3
4	addr3		data4
5	clock_change_mode		data5
6	clock_max_count		data6
7			data7

514 Tiny Eater 8 Bit