---
title: "Photon"
id: 72036
type: "computer_media"
slug: "photon"
url: "http://localhost/computer_media/photon/"
markdown_url: "http://localhost/computer_media/photon.md"
published_at: "2026-10-20T14:07:37+00:00"
modified_at: "2026-10-20T14:19:54+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2026/10/3_PHOTON.png"
excerpt: "A machine code light beam bounces diagonally around a black box, tracing a criss-cross path of white squares before the pattern clears and restarts."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
indiv:
  - name: "Gene G. Buza"
    slug: "gene-g-buza"
    taxonomy: "indiv"
    url: "http://localhost/indiv/gene-g-buza/"
genre:
  - name: "Graphics"
    slug: "graphics"
    taxonomy: "genre"
    url: "http://localhost/type/graphics/"
media_contents:
  - id: 72046
    title: "Synchro-Sette May 1984"
    type: "computer_media"
    url: "http://localhost/computer_media/synchro-sette-may-1984/"
media_type: "Program"
programmers:
  - name: "Gene G. Buza"
    slug: "gene-g-buza"
    taxonomy: "indiv"
    url: "http://localhost/indiv/gene-g-buza/"
mediadate: "1984"
images:
  - url: "http://localhost/wp-content/uploads/2026/10/3_PHOTON.png"
media_type_tags: "Graphics"
---

# Photon

A graphics display in which a beam of light travels diagonally across a black field and reflects off its edges, leaving a trail of white squares that builds up into a criss-cross pattern. When the run finishes, the program clears itself and starts a new pattern from a different starting value.

***

## Program Analysis

### Program Structure

The work is done by a machine code routine stored in the `REM` at line 0, which the listing shows only as keyword and character noise. The BASIC part is a short driver:

- Line 10 calls the routine at 16533 with `RAND USR 16533`, apparently to set up the field and its border.
- Line 30 POKEs a random value from 10 to 41 into address 16571, a byte inside the machine code just before the second entry point, so each run starts differently.
- Lines 40–60 fill sixteen rows with full blocks to make the black playing field.
- Line 70 runs the beam routine with `RAND USR 16572`. Lines 80–90 then `CLEAR` and `RUN 10` to start the next pattern.

The machine code itself has not been disassembled for this description.

### Notable Techniques

- The BASIC program changes the machine code’s behaviour by POKEing one byte of the `REM` before each run, a common way to pass a value to a ZX81 routine.
- The program is saved to start with `RUN 10`, which skips line 0.

## Source Code

```
   0 Y[▒]▞4NOT ( CLEARTAN Y)[(]#LN  PRINT ▒Y[▒]NOT TAN LN F?LN E~~LN ▙RND▞(VAL : LN [~~]RNDAT VAL :3LN [~~]RNDAT ( LIST Y#WNOT LN ▙RNDTAN ▘ COPY1~~Y▘M[S]RNDM[T]RNDWM[U]RND GOSUB #[U]RNDY[.]MKRNDLN [M]"LN [V]▝ FOR 5 CLS LOAD [B] GOSUB #COS 5# CLEAR[B] GOSUB #COS U[U]RND RETURN▝C▖ RETURNX4▒U[T]RNDJWM[T]RNDU[V]RND RETURN~~C▖ RETURND4▒U[S]RNDJWM[S]RND GOSUB #[U]RNDY[4]MKRNDLN [M]"5[T]RND▘[U]RND~~[-]▝F▀~~[-]▝/[4]
  10 RAND USR 16533
  20 PRINT AT 19,9;"█[P]█[H]█[O]█[T]█[O]█[N]█"
  30 POKE 16571,INT (RND*32+10)
  40 FOR N=1 TO 16
  50 PRINT AT N,1;"██████████████████████████████"
  60 NEXT N
  70 RAND USR 16572
  80 CLEAR
  90 RUN 10
9998 SAVE "PHOTO[N]"
9999 RUN 10
```