---
title: "Matrix Drawing"
id: 76520
type: "computer_media"
slug: "matrix-drawing"
url: "http://localhost/computer_media/matrix-drawing/"
markdown_url: "http://localhost/computer_media/matrix-drawing.md"
published_at: "2026-11-11T08:02:36+00:00"
modified_at: "2026-11-11T08:02:36+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2026/11/matrix-drawing-1.png"
excerpt: "Build a picture one character at a time on a 13 by 20 grid by typing a row, a column and a character code."
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "ZX80"
    slug: "zx80"
    taxonomy: "post_tag"
    url: "http://localhost/tag/zx80/"
model:
  - name: "Sinclair ZX80"
    slug: "zx80"
    taxonomy: "model"
    url: "http://localhost/model/zx80/"
indiv:
  - name: "Robert Ryan"
    slug: "robert-ryan"
    taxonomy: "indiv"
    url: "http://localhost/indiv/robert-ryan/"
genre:
  - name: "Graphics"
    slug: "graphics"
    taxonomy: "genre"
    url: "http://localhost/type/graphics/"
media_type: "Program"
programmers:
  - name: "Robert Ryan"
    slug: "robert-ryan"
    taxonomy: "indiv"
    url: "http://localhost/indiv/robert-ryan/"
download_url: "https://archive.org/download/timex-sinclair-software-archive/Matrix%20Drawing%20%281981%29%28Ryan%2C%20Robert%29%28ZX80%29%28US%29%28Program%29.zip"
mediadate: "1981"
images:
  - url: "http://localhost/wp-content/uploads/2026/11/matrix-drawing-1.png"
  - url: "http://localhost/wp-content/uploads/2026/11/matrix-drawing-2.png"
  - url: "http://localhost/wp-content/uploads/2026/11/matrix-drawing-3.png"
article_media:
  - id: 19727
    title: "Matrix Drawing"
    type: "article"
    url: "http://localhost/article/matrix-drawing/"
media_type_tags: "Graphics"
license: false
---

# Matrix Drawing

Draws characters on a 13 by 20 grid. The program keeps the grid in memory from address 20000 up, fills it with inverse spaces and prints it, then asks for a row (1-13), a column (1-20) and a character code. It POKEs the code into the grid, clears the screen and reprints, so you build the picture one character at a time.

Written for the 4K ROM; the article notes that 8K users must change the POKE addresses to spare memory. Needs at least 4K RAM for the grid at 20000.

Published in Syntax June 1981 ([Matrix Drawing](https://timexsinclair.com/article/matrix-drawing/)).

## Source Code

```
   1 LET A=19999
   6 LET V=0
  10 FOR I=1 TO 13
  20 FOR J=1 TO 20
  30 IF V>0 THEN GO TO 50
  40 POKE A+(I*20)+J,128
  50 PRINT CHR$(PEEK(A+(I*20)+J));
  60 IF J=20 THEN PRINT " "
  70 NEXT J
  80 NEXT I
  90 INPUT D
 100 INPUT B
 110 INPUT C
 120 POKE A+(D*20)+B,C
 130 CLS
 131 CLEAR
 135 LET V=1
 137 LET A=19999
 140 GO TO 10
```