Gridtrap

Gridtrap
Title screen of the game
Game No.	514
Voting	6.80 points, 5 votes
Company	Livewire
HVSC-File	/GAMES/G-L/Gridtrap.sid
Release	1983
Platform	Amstrad CPC, Atari 400/800, C64, C16, Plus/4, VC-20, ZX Spectrum, MSX
Genre	Arcade
Gamemode	Single player 2 players (in turns)
Operation
Media
Language
Information	Released in 1982 for the VC-20

Description

Mr. Livewire

In the game "Gridtrap", the player controls the character "Mr. Livewire" across a game board with 15×10 square tiles, collecting flags and defusing 5 time bombs in each level. He may only enter each tile once, so careful route planning is essential. Along the way, he must avoid collisions with boots that move randomly across the board and must steer clear of certain tiles marked with skulls. Colliding with a boot or a skull costs the character one of his initial three lives (see the left animation in the gallery below). After successfully deactivating all 5 bombs, the next level begins with a new game board.

Route planning on the game board is made easier by the fact that when the character crosses any edge of the board, he reappears on the opposite side (right animation, at the start of the game). Furthermore, the character can sometimes escape from otherwise hopeless situations by pushing new, unoccupied spaces into the current row of the game board (middle animation).

Mr. Livewire moves across the game board, space by space... as long as he doesn't collide with a boot or skull!

If the character has maneuvered himself into a dead end, new spaces can potentially be pushed in horizontally.

By taking shortcuts across the edges of the game board, the first level can be completed in just 14 seconds.

Design

During the game, most of the screen is occupied by the game board, which is always visible in its entirety. Only the top four lines of text are reserved for displaying the score; on the right side of the screen, a cage is visible, in which up to three boots are imprisoned in the first few levels. These boots are then used gradually as the game progresses. The graphics are colorful and well-coordinated, making the game visually appealing from the start.

Graphics

The game uses multicolor text mode throughout (video RAM at address $0400, character set at $3800). The player character, the four boots, and the numbers indicating the remaining time until the bombs explode are sprites; all other graphic elements are part of the text display.

Sound

A two-part background melody plays continuously during gameplay. It is relatively short, therefore repeats quickly, and consequently becomes monotonous after a short time—fortunately, it can be turned off with the press of a button (see section "Controls"). In-game events, such as collecting flags or defusing bombs, are also accompanied by short, monophonic sound sequences.

Sound of footsteps

Picking up a flag

Collision with a boot

Kick from a boot

Hints

Time bomb

After the intro, the scoring system and controls are briefly explained.

The goal of the game "Gridtrap" is to defuse five time bombs in each level before they explode 30 seconds after appearing. The player-controlled character, "Mr. Livewire," is placed in the upper left corner of a 15 × 10 square game board, from where he moves to the time bombs. These appear on the game board every 15 seconds, or at the latest after all previous bombs have been defused.

Most spaces on the game board are covered with turquoise tiles at the start of a level and can be entered by Mr. Livewire—but only once, because the tile disappears upon entry! Therefore, the route to each bomb must be carefully planned to ensure that the character's path isn't blocked by paths already taken. If this does happen, it can help to shift the row of the game board where the character is currently located, step by step, to the left or right. The newly appearing spaces on the game board are then covered with tiles and can be entered. However, this only works if shifting the tiles doesn't push a flag, skull, or bomb out of the game board or underneath the player character.

An increasing number of spaces are marked with skulls from the start and cannot be entered, as doing so causes the character to lose a life. Furthermore, each game board contains four flags that can be collected; the points awarded for each flag increase linearly: from 500 points for the first to 2000 points for the fourth flag. The points awarded for defusing a time bomb are calculated by multiplying the number of seconds remaining until the explosion by 100, and thus range from 100 to 3000 points.

If the player manages to defuse all five bombs in time, they advance to the next, more difficult level and can try their luck with five more time bombs. However, at the start of each of the first four levels, another boot leaves the cage on the right side of the screen where it was previously imprisoned and begins to wander around the game board. If Mr. Livewire collides with one of these boots or a skull, or if one of the time bombs explodes, the character loses a life and must try again on the same level with a new game board. An extra life is awarded every 100,000 points.

Screen Layout

Typical scene from the game

Controls

"Gridtrap" can be controlled either with a joystick in port 2 or with the keyboard. The game can be started by pressing the fire button or the F7  key. Unless otherwise configured in the settings menu, the following actions will then apply:

• and or Z  and C : The character moves left or right
• and or ,  and / : The character moves up or down
• and or .  and X : The row in which the character is located is moved left or right and filled with new spaces
• P : Pause (resume by pressing P  again)
• N : Turn off music
• M : Turn on music
• V : Play a short demonstration

Before the game starts, you can select the number of players and set the difficulty level on a scale of 1 to 9; the latter determines what percentage of the spaces are blocked by skulls, how fast the boots move across the playing field, and how quickly the time bombs' clocks run out (left animation in the gallery below). This input screen opens when you press the F5  key during the intro. Pressing F3  allows you to set the number of players; you can choose between a single player or two players taking turns. Pressing F5  increments the difficulty level.

Pressing F1  restarts the game; in particular, you must then configure the keys used to control the character. To do this, press the keys in succession that will move the character or scroll in the currently displayed direction. If the key is valid (i.e., not already assigned to another function), the message "OK" appears, and the next assignment is requested (right animation); otherwise, the program waits for an alternative, valid key.

Pressing F5 allows you to adjust the number of players and the difficulty level.

Pressing F1 allows you to change the keyboard layout.

Tips

• When planning your route, it is recommended to always head first for the bomb with the shortest remaining time and only collect flags if they are directly on or near the way there. Only when the fifth and final bomb remains can you reliably assess which flags are still reachable with the remaining unoccupied spaces—and you should then collect these.
• By crossing the right, top, and bottom edges of the playing field, you can also move to the other side of the playing field even if there is only a space you have already occupied there. Whether this behavior is a programming error that the authors noticed but never fixed, or whether this functionality was planned from the beginning, is of course impossible to determine—however, it is explicitly mentioned in the documentation and can occasionally be useful.

Solution

"Gridtrap" does not have a solution where, for example, all the bombs are defused in the end and Mr. Livewire is honored for his heroic efforts. Rather, it is simply about playing the game for as long as possible and accumulating as many points as possible.

Cheats

In the CSDb there is a crack of Commo Bam with a trainer function. Its only option is to grant the player character unlimited lives:

Crack with trainer function of Commo Bam

Alternatively, trainer functions can also be achieved by modifying the game's machine code after loading it by entering POKE commands before starting it with RUN. Since the program code is copied after loading before the game starts, such POKEs depend on the crack used; For the Crack by Duplosoft, the following list, for example, offers a number of interesting trainer functionalities that can be used independently:

POKE 18892,173 : POKE 21804,173 : POKE21864,173 : REM INFINITE LIVES
L=7 : POKE 20745,L : REM L INSTEAD OF 3 LIVES AT THE  START OF THE GAME, L=1..9
S=1 : POKE 20807,S+1 : POKE 22957,S : REM AT MOST S HIKING BOOTS, S=1..4
B=3 : POKE 20794,B : REM DEFUSING B BOMBS PER LEVEL, B=1..255

Internal Data Structures

For developing custom trainer functions and for analyzing or manipulating the data used by the game, knowledge of memory allocation and internal workings is helpful. The following table therefore compiles a range of information about "Gridtrap".

Address	Content	Comments
$0364	Number of hiking boots player 1	1..4
$038E	Number of hiking boots player 2	1..4
$036C	Number of lives player 1	1..9
$036D	Number of lives player 2	1..9
$036F	Number of collected flags	0..4
$039C	Number of collected bombs	0..5
$0390—$0395	Score player 1	Most significant digit first, $04="0"..$16="9"
$0396—$039B	Score player 2	Most significant digit first, $04="0"..$16="9"

Votes

Voting of the C64-Wiki users (10=the best vote):
6.80 points at 5 votes (rank 549). You need to be logged in to cast a vote.
C64Games	7	June 20, 2006 - "sehr gut" - 2989 downs
Lemon64	6.67	April 13, 2025 - 16 votes
Ready64	6,00	April 13, 2025 - 1 voto
Personal Computer Games	7/10 (Graphics 6/10, Sound 6/10, Ease of use 8/10, Originality 5/10, Lasting interest 6/10)	April 1984
Your Commodore	2/5	October 1984
Home Computing Weekly	4/5 (instructions 70%, playability 60%, graphics 80%, value for money 80%)	January 24—30, 1984
MSX Computing	2/3 (Graphics 2/3, Sound 1/3, Value 3/3)	October/November 1985
Universal Videogame List	3.2/5	April 13, 2025
Rombachs C64-Spieleführer	8	September 1984 - "Verdict 2"

Critics

Stephan64: "Gridtrap demands a balanced mix of reaction time and strategic planning from the player. Visually appealing and with the right level of difficulty, it can keep players engaged for extended periods. The only drawback is that when collecting flags and defusing bombs, the player character remains stuck on the respective square until the accompanying music has finished, which makes the controls feel somewhat clunky. Nevertheless, considering its early release year, I give it 6 points."

Rombachs C64-Spieleführer: "An interesting action game with strategy elements (Verdict 2)."

Miscellaneous

Cover

Cassette cover

Inlay

Cassette inlay, outside

Cassette inlay, inside

Cassette

Cassette for the game "Gridtrap"

Theme

The following image shows the game's theme song in standard musical notation. For creative use of the music, the sheet music is also available as a PDF document (File:Gridtrap Theme PDF.pdf) and in ABC musical notation (File:Gridtrap Theme.abc.txt).

​​Musical notes of the accompaniment melody, reconstructed by logging all write accesses to the SID

Fastloader

The cassette version of "Gridtrap" uses an integrated software fast loader, which is partially located in the header of the program stored on the cassette and is thus transferred to the cassette buffer as soon as the first part of the program is located. It also occupies part of the space reserved for the filename; however, this is not usually visible on the screen because it is preceded by the character code $1F (PETSCII code for "dark blue font color"). If, however, the background color is changed before loading "Gridtrap," the beginning of the loading routine becomes visible on the screen (see figure below).

The first part of the program itself contains only the routines for reading a single bit and, based on this, for reading a byte, as well as for initialization. During the loading process, the screen display is turned off; because the border color changes after each byte is read, the screen displays a colorful, flickering striped pattern during this time. Thanks to optimized encoding (shorter intervals for 0 and 1 bits, no parity bit, no duplicate storage of program data), loading Gridtrap takes only about 70 seconds, whereas the KERNAL's datasette routines would take more than 7 minutes for a program of this size.

The routines for synchronization and for reading a bit and a byte are identical to those in the fast loader of the game "Aquanaut (Interceptor)", and largely identical to those of "Elidon" and "Loco". In contrast to the fast loaders of these games, the one for "Gridtrap" appears rather chaotic: The synchronization routine is called twice before the actual loading process; it unnecessarily checks for the presence of a (non-existent) second program block; the checksum is calculated but not compared with the correct value; and at the end of the loading process, the recorder is not stopped but started again.

If you change the background color before loading, the beginning of the loading routine becomes visible as the filename.

Video Recording

Short demonstration of the game

Bugs

The game contains a few minor inconsistencies that, while not detracting from the fun, were certainly not intended by the program's authors. For example, a collision between Mr. Livewire and a walking boot is not recognized as such if both characters move toward each other at the same time (left animation in the gallery below). Also puzzling is the fact that the space currently occupied by the player character is covered with a turquoise tile when scrolling left or right along the corresponding row of the game board.

A collision between the game character and a boot is not detected.

When a line is moved left or right, a tile appears under the character.

Trivia

Included with the game was an entry form for a prize draw in which the ten users of the game who reported the highest high scores could win a Commodore 1541 floppy disk drive, a VC-1520 plotter, a cartridge of Simons' BASIC, and seven joysticks. The offer was only available to users in Great Britain. The deadline for entries was March 1, 1984:

Front of the competition entry form

Back of the entry form

To verify the authenticity of the high score achieved, a "Magic Number" is always displayed at the end of the game along with the current highest score. This "Magic Number" must match the high score. The procedure used to determine this checksum appears at first glance to be highly complex and therefore well protected against manipulation: It involves three successive, indexed memory accesses to tables of constants in the address ranges $4391–$43C7, $1D00–$1DFF, and $1C00–$1CFF.

However, only the checksum of the highest score achieved (stored at address $40BA–$40BF) is used in this procedure; two different high scores with the same checksum are therefore always assigned the same "Magic Number." So, those who calculated their chances of winning a prize with their best score of 980 points (and Magic Number "180") might have had better luck if they simply entered a high score of "980,000" (with the same "Magic Number") on the entry form. When cheating, the only requirement was that the reported high score had to be an integer multiple of 20.

A meager high score of 980 points yields the checksum "180"...

... but manipulation using a debugger shows that the same checksum results for 980,000 points.

Highscore

The following list invites you to immortalize yourself with your highest score. "Gridtrap" can be played at any difficulty level. Since the score count resets to 0 when exceeding 999,980 points, it is recommended that very good players take a screenshot for the high score list shortly before reaching 1 million points.

Topscore of Stephan64

1. Stephan64 - 143.520 (18.04.2025)
2. Keiner - 0 (tt.mm.jjjj)
3. Niemand - 0 (tt.mm.jjjj)

	#2 Keiner		#3 Niemand

Links

• Gamebase64.com - Game No. 3298
• CsDB (all entries)
• CSDb - Release No. 194336, CSDb - Release No. 114256
• Lemon64 - Game No. 1107
• ready64 - Game No. 4343
• Gridtrap at MobyGames

• Universal Videogame List

Magazine

• Home Computing Weekly test report (p. 36)
• Your Commodore test report (p. 37)
• Personal Computer Games test report (pp. 55)
• MSX Computing test report (p. 63)