Recreating Atari Pong 1972 - The Heart of the Machine and H-Timing

Imagine you have to create a video game. A moving ball, two paddles bouncing it back and forth, scorekeeping, the sound of the ball being hit, and an image displayed on a television screen.

The first thought of a modern programmer? Python, C++, Unity, or perhaps a simple JavaScript script running on a Canvas.

Now imagine going back in time to 1972.

You have no processor (the Intel 8080 doesn`t even exist yet).
You have no RAM.
You have no disk, graphics card, or operating system.
You can`t write a single line of code.

Under these conditions, 24-year-old engineer Allan Alcorn created the legendary game "PONG" at Atari — an arcade machine that helped launch the entire modern video game industry.

How did he do it?

Using nothing but discrete digital logic integrated circuits from the "7400 TTL series" — pure physics, logic gates, and flip-flops.

I decided to take on the challenge myself: to recreate the original Pong circuitry step by step in "Atanua", a real-time digital logic simulator, and see how this magic actually worked under the hood.

Welcome to the first episode of the series, where we`ll build the foundation of the entire arcade machine — the "Horizontal Timing Generator (H-Timing)".

How does the machine know where the ball is if there is no processor?

A modern game has a "game loop" that calculates the position of objects (X, Y) every frame.

In 1972, there was no memory storing pixel coordinates. The image on a CRT was generated by an electron beam scanning the screen line by line — from left to right and from top to bottom.

The entire "game" in Pong is, in reality, a precise digital clock counting timing pulses that control the CRT beam.

When the counter reaches the exact moment at which the electron beam is at the position of a paddle or the ball, the logic circuitry enables the video signal, illuminating that particular point on the screen.

That`s why we start with the X axis — the horizontal line timing generator.

A look at the original schematic

In the original 1972 Pong schematic, the horizontal timing section is based on integrated counter chips (such as the "7490" and "7493" driven by the arcade machine`s master clock.



Fragment of the original Atari Pong schematic showing the horizontal timing section.

Each counter output divides the clock frequency by 2, giving us the horizontal position bits:

"1H, 2H, 4H, 8H, 16H, 32H, 64H, 128H, 256H."

Step 1: Building the H-Timing Generator in Atanua

For our reconstruction, we`re using "Atanua", a real-time digital logic simulator.

Here`s how our circuit works

"Base clock" A pulse generator (slowed down to 10 Hz for demonstration purposes, or clocked manually using the "C" key so that we can see the logic states with our own eyes).

"Flip-flop cascade (1H to 256H)" 9 T-type flip-flops connected in series. Each successive flip-flop changes state twice as slowly as the previous one, creating a 9-bit binary counter counting from 0 to 511.

#The magic number 454 — End of Line / H-RESET

The NTSC television standard requires a single horizontal line to last exactly "454 clock cycles".

We can decompose 454 into powers of two:

\(454 = 256 + 128 + 64 + 4 + 2\)

AND gates check whether the "256H, 128H, 64H, 4H, and 2H" outputs are simultaneously active.

When the counter reaches 454, the logic generates an "H-RESET" pulse, immediately resetting the counter to zero and starting a new line.

"Beam blanking (H-BLANK)" When the counter passes position 384, the CRT beam is blanked while it returns to the left side of the screen — hence the yellow blanking LED.

The circuit in action!

Below you can see how the circuit behaves in the simulator. Pay attention to the green LEDs counting in binary and the red "H-RESET" LED, which flashes precisely after 454 clock cycles:


Visualization of horizontal timing — binary pixel counting and the end-of-line pulse.

What`s next?

We now have a working time base for the horizontal (X) axis.

The same "H-RESET" pulse that resets our line will serve as the clock signal for the next block.

In the next episode, well build the "Vertical Synchronization Generator (V-Timing)". This will give the machine awareness of the vertical (Y) axis and allow it to count the screen lines from top to bottom.

Stay tuned — in the upcoming parts we`ll add the playing-field grid, paddle controls, ball-bouncing physics, and finally connect the sound generator!

"What do you think about this approach to retro engineering? Let me know in the comments below!"