---
title: "Joystick Wrapper"
id: 56105
type: "computer_media"
slug: "joystick-wrapper"
url: "http://localhost/computer_media/joystick-wrapper/"
markdown_url: "http://localhost/computer_media/joystick-wrapper.md"
published_at: "2024-07-19T01:29:08+00:00"
modified_at: "2026-03-30T21:43:23+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/07/SCR-20240718-sphf.png"
excerpt: "A joystick demo moves a cursor around the full screen with edge wraparound and diagonal movement, all packed into a handful of clever BASIC expressions."
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/"
indiv:
  - name: "Martin DeBoniface"
    slug: "martin-deboniface"
    taxonomy: "indiv"
    url: "http://localhost/indiv/martin-deboniface/"
genre:
  - name: "Demo"
    slug: "demo"
    taxonomy: "genre"
    url: "http://localhost/type/demo/"
  - name: "Programming"
    slug: "programming"
    taxonomy: "genre"
    url: "http://localhost/type/programming/"
media_type: "Program"
programmers:
  - name: "Martin DeBoniface"
    slug: "martin-deboniface"
    taxonomy: "indiv"
    url: "http://localhost/indiv/martin-deboniface/"
download_url: "https://archive.org/download/timex-sinclair-software-archive/JoystickWrap%20%28198x%29%28TS2068%29%28US%29%28Program%29.zip"
mediadate: "1985"
images:
  - url: "http://localhost/wp-content/uploads/2024/07/SCR-20240718-sphf.png"
media_type_tags: "Demo, Programming"
---

# Joystick Wrapper

This program demonstrates joystick-controlled cursor movement with wraparound behavior on a 32×22 character grid, using the STICK function to read a joystick input. A single asterisk character is moved around the screen by polling the joystick direction codes (1–10), with diagonal movement supported. The wraparound logic uses a compact BASIC expression combining OR and AND operators to detect screen boundaries and loop the cursor from one edge to the opposite edge. A FIRE button check via STICK’s second parameter displays the word “FIRE” at a fixed position when pressed.

***

## Program Analysis

### Program Structure

The program is a tight main loop occupying lines `300`–`400`, with a `SAVE`/`VERIFY` utility at line `410`, a `STOP` at `420`, and an embedded reference comment at line `430` that documents all variable names. Execution begins at line `300` (a REM), initializes column `c` and line `l` to 10, then enters the display/input loop at line `320`.

### Joystick Reading

Lines `340` and `350` use the TS2068 `STICK` keyword to read the joystick. `STICK(1,2)` returns the directional value of joystick 1 into `s`, and `STICK(2,2)` returns the fire-button state into `b`. The direction codes used are:

| Code | Direction |
| --- | --- |
| 1 | Up |
| 2 | Down |
| 4 | Left |
| 5 | Up-Left |
| 6 | Down-Left |
| 8 | Right |
| 9 | Up-Right |
| 10 | Down-Right |

### Wraparound Logic

Lines `360` and `370` contain the most technically interesting code in the program. Each uses a pair of compound boolean expressions to both move the coordinate and implement wraparound. Consider the column update on line `360`:

`LET c=c+((-31 OR c<31) AND (s=8 OR s=9 OR s=10))-((-31 OR c>0) AND (s=4 OR s=5 OR s=6))`

In Sinclair BASIC, boolean expressions evaluate to 1 (true) or 0 (false), and `OR` between a numeric value and a boolean acts as addition when combined with `AND`. The sub-expression `(-31 OR c<31)` evaluates to `-31` when `c<31` is false (i.e., `c=31`), effectively wrapping the column back by 32 positions; when `c<31` is true, it evaluates to `-31+1 = -30`… actually, more precisely: since boolean TRUE=1 and FALSE=0, `-31 OR c<31` computes as `-31 + (c<31)`. When `c<31`, this is `-31+1=-30`, but multiplied by the direction AND term the net effect is +1 or -31 respectively, giving normal movement or wraparound. The same pattern is mirrored for line `l` on line `370` using limits of 21 and 0.

### Efficient Screen Update

Line `390` uses the string-AND idiom: `PRINT AT ll,cc;" " AND (ll<>l OR cc<>c)`. The expression `" " AND condition` prints a space (erasing the old cursor position) only when the cursor has actually moved, avoiding unnecessary screen writes when the joystick is centered. This requires saving the previous coordinates into `cc` and `ll` at line `330` before updating.

### Fire Button Display

Line `380` uses the same string-AND technique to display the word `FIRE` at screen position `AT 9,9` only when `b=1` (button pressed). When the button is not pressed, the expression evaluates to an empty string, effectively printing nothing — though this does not erase a previously displayed “FIRE”. This is a minor display anomaly: once displayed, “FIRE” will persist on screen until the button is pressed again on the next polling cycle.

### Key BASIC Idioms

- Boolean arithmetic (`AND`/`OR` returning 0/1) used as conditional multipliers
- `string AND condition` for conditional printing without `IF` statements
- Saving prior coordinates to minimize `PRINT` calls
- All logic condensed into a handful of lines for a fast polling loop

### Variable Summary

The inline documentation at line `430` lists all variables, reproduced here for clarity:

| Variable | Meaning | Range |
| --- | --- | --- |
| `c` | Current column | 0–31 |
| `l` | Current line | 0–21 |
| `cc` | Previous column | — |
| `ll` | Previous line | — |
| `s` | Stick direction value | — |
| `b` | Button (FIRE) value | — |

## Source Code

```
  300 REM Joy Stick Wrap around    © Martin DeBoniface 30/09/85  
  310 LET c=10: LET l=10
  320 PRINT AT l,c;"*"
  330 LET cc=c: LET ll=l
  340 LET s=STICK(1,2)
  350 LET b=STICK(2,2)
  360 LET c=c+((-31 OR c<31) AND (s=8 OR s=9 OR s=10))-((-31 OR c>0) AND (s=4 OR s=5 OR s=6))
  370 LET l=l+((-21 OR l<21) AND (s=2 OR s=6 OR s=10))-((-21 OR l>0) AND (s=1 OR s=5 OR s=9))
  380 PRINT AT 9,9;"FIRE" AND b=1
  390 PRINT AT ll,cc;" " AND (ll<>l OR cc<>c)
  400 GO TO 320
  410 SAVE "JoySTICKWrapAr": PRINT #0;AT 0,5;"Rewind ";"Tape to Verify ": VERIFY "JoySTICKWrapAr"
  420 STOP 
  430 REM                                     INDEX                                                  Meaningful Variable Names                                    c  = column             (0-31)  l  = line               (0-21)  cc = concurrent c value         ll = last l value               s  = stick value                b  = button value       (FIRE)
```