What is it?

It refers to 4-bit CPU projects with discrete logic such as TD4-CPU and Cute-CPU, improves the previous instruction and machine code encoding methods, reduces the size, and simplifies the structure of a 74-chip discrete CPU product.

Why did you make it?

What makes it special?

The basic parameters are as follows:
ROM: 4k x 8bit;
RAM: 1k x 4bit;
I/O: 16 x 4bit (4-bit address line);
Register group: ACC (main operand), B (secondary operand), C register, three addressing registers A2, A1, and A0. Can address 4kB of program space or 1kB of RAM. IO port addressing is completed independently by the A0 register. No stack

Built-in fixed IRC oscillator, clock frequency ≥1KHz; you can also select buttons to input clock pulses. The operation part is built around 74LS181 and has two flag registers, CF and ZF.
The basic instructions are all single-cycle: addition, subtraction, negation, exclusive OR, identical OR, bitwise AND, comparison, data transfer, immediate data storage in register, IO input and output, RAM access, jump, PSW conditional jump wait.
In addition to the motherboard, you can also connect external displays/button arrays, etc. The IO port of the motherboard reads and writes peripherals with standard 6800 bus timing (4-bit data); this largely makes up for the shortcomings of the TD4-CPU in human-computer interaction. , which improves the shortcoming of Cute-CPU with few external expansion IO ports and effectively improves the user experience.