Before you start

This kit is a sequel to the "A Watch and a Game from Gates" kit and does not work without it. The processor is built next to the machine from the first kit (the game with the watch) and takes its screen, buttons, 60 Hz hardware and parts library. Complete the first kit first, then this one.

In the first kit, "A Watch and a Game from Gates", we built a watch and the game "Star Harvest" entirely from gates and flip-flops: every part of the game had hardware of its own. A real Game & Watch is built differently inside: it has a small processor (the Sharp SM5) and a program in ROM. Now we do the same: we build our own 4-bit processor and move the watch and the game onto it.

What we build

A processor with an accumulator A, flags Z and C, a program counter, a data memory of 256 cells and a ROM of 512 instructions. 16 instructions, from LD to RET. The screen, the buttons, the step timer and the randomness are the same as in the first kit's game, only now a program is in charge of them.

By the end of lesson 6 the same game runs as a program on your processor. In lesson 7 you learn to program, from scratch, even if you have never done it before, and in lesson 8 you write a game yourself.

How the kit is organised

Each lesson gives the processor one new ability and shows it on the machine right away:

  • lesson 1: the A register and the ALU — a calculator on switches;
  • lesson 2: the program counter and the ROM — lights running through a program;
  • lesson 3: data memory and screen memory — digits on the LCD from a program;
  • lesson 4: jumps — a 0–9 counter as a program;
  • lesson 5: subroutines, ports, the "second" flag — a watch as a program;
  • lesson 6: the game screen, the step timer, randomness, the beep — the game as a program;
  • lesson 7: first programs — you learn to write in assembly and check your work right in the book;
  • lesson 8: you write a game yourself.

What you need from the first kit: the whole chapter 2 machine (the game with the watch) and its library — the gates, MUX2, DFF, DEC4x1, AND3, AND4, OR3 and the game hardware (CNT60, CNT16, LFSR8, SPEED, SHIFT5). We don't throw the old parts away at once: the processor is built alongside, and the parts of the game leave one at a time, as the program takes over their work.

Simulator mode. You can build and check the circuit in REAL, but play in Fast: the processor does everything one step at a time, and it needs a fast clock (why — see the kit summary).