---
title: "Joystick"
id: 71254
type: "computer_media"
slug: "joystick-2"
url: "http://localhost/computer_media/joystick-2/"
markdown_url: "http://localhost/computer_media/joystick-2.md"
published_at: "2026-08-30T17:34:10+00:00"
modified_at: "2026-08-30T17:34:11+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2022/04/20230809-041332.jpg"
excerpt: "Guide a randomly colored symbol anywhere on screen using joystick directional values, with boundary checking and a second button to randomize the character itself."
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 2068"
    slug: "ts2068"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts2068/"
model:
  - name: "Timex/Sinclair 2068"
    slug: "ts-2068"
    taxonomy: "model"
    url: "http://localhost/model/ts-2068/"
genre:
  - name: "Joystick"
    slug: "joystick"
    taxonomy: "genre"
    url: "http://localhost/type/joystick/"
media_type: "Program"
download_url: "https://archive.org/download/timex-sinclair-software-archive/joystick%20%28198x%29%28-%29%28TS2068%29%28US%29%28Program%29.zip"
mediadate: "198x"
media_type_tags: "Joystick"
---

# Joystick

This program moves a copyright symbol (©) around the screen using a joystick, reading STICK values to detect directional input. The cursor position is tracked in variables A (row) and B (column), with boundary clamping applied to keep within the 22-row by 32-column display area. Each iteration redraws the character with a randomly chosen INK color (0–6) via `INT(RND*7)`. A second joystick trigger (STICK 2) allows the displayed character to be changed to a random printable character in the range CHR$(91)–CHR$(143).

***

### Program Structure

The program is a short main loop that reads joystick input and repositions a character on the screen. Initialization at lines 10–20 sets the row (`A`), column (`B`), and display character (`Z$`) to their starting values. Lines 30–80 form the core loop: print, then test each directional STICK value and update position accordingly. Line 90 handles a fire/button event on a second joystick port to randomize the character. Line 100 jumps back to line 30 unconditionally.

### STICK Value Decoding

The `STICK(1,2)` call returns a bitmask representing the joystick directions. The values tested correspond to the following directional combinations:

| STICK value | Meaning |
| --- | --- |
| 1 | Up |
| 2 | Down |
| 4 | Left |
| 8 | Right |
| 5 | Up + Left |
| 6 | Down + Left |
| 9 | Up + Right |
| 10 | Down + Right |

Each directional line (50–80) tests three STICK values: the cardinal direction and two diagonals that include that component. This correctly handles diagonal joystick movement by updating both axes independently across consecutive IF checks.

### Boundary Clamping

After each position update, the new value is checked against the display limits: row `A` is clamped to 0–21 and column `B` to 0–31, matching the 22×32 character grid. When a boundary is hit, the value is reset to the limit and execution jumps directly to line 30 via `GO TO 30`, skipping the remaining directional checks for that frame.

### Display Technique

Line 30 prints `Z$` at position (`A`,`B`) with a randomly selected INK color on every iteration. Because there is no `PRINT AT` to erase the previous position, the character trail remains on screen, progressively painting the display as the symbol moves. The `FLASH 0` at line 40 ensures flashing is suppressed each cycle, though it has no functional effect unless FLASH was previously set.

### Character Randomization

Line 90 reads a second joystick port via `STICK(2,2)` and, when value 1 is detected, replaces `Z$` with a random character using `CHR$(INT(RND*53)+91)`. This generates characters in the range CHR$(91) to CHR$(143), which spans symbols, lowercase letters, and the lower block graphics characters.

### Notable Anomalies

- Line 50 checks `STICK(1,2)=5` (Up+Left) for the Up handler, and line 60 also checks `STICK(1,2)=5` for the Left handler. When the joystick is at Up+Left (value 5), both A and B are decremented correctly because each IF is evaluated independently.
- The display is never cleared between frames, so the moving character leaves a colored trail across the screen rather than appearing to move cleanly.
- The initial value of `Z$` is set to the © character (the zmakebas `\*` escape), which is a block graphic rather than a printable ASCII symbol.

## Source Code

```
  10 LET A=0:LET B=A
  20 LET Z$="\*"
  30 PRINT AT A,B; INK INT (RND*7);Z$
  40 FLASH 0
  50 IF STICK (1,2)=1 OR STICK (1,2)=5 OR STICK (1,2)=9 THEN LET A=A-1:IF A<0 THEN LET A=0:GO TO 30
  60 IF STICK (1,2)=4 OR STICK (1,2)=6 OR STICK (1,2)=5 THEN LET B=B-1:IF B<0 THEN LET B=0:GO TO 30
  70 IF STICK (1,2)=2 OR STICK (1,2)=10 OR STICK (1,2)=6 THEN LET A=A+1:IF A>21 THEN LET A=21:GO TO 30
  80 IF STICK (1,2)=8 OR STICK (1,2)=10 OR STICK (1,2)=9 THEN LET B=B+1:IF B>31 THEN LET B=31:GO TO 30
  90 IF STICK (2,2)=1 THEN LET Z$= CHR$ (INT (RND*53)+91)
 100 GO TO 30
```