Thrust

01 · Controls

Secret: the C64 copy keeps the BBC Micro's key page

On the C64 the ship is flown from the keyboard. A and S turn it through 32 directions, either Shift key thrusts, Return fires, and Space raises the shield, which is also the tractor beam. F5 pauses until F7 is pressed, and F1 and F3 turn the sound off and on.

The game reads the whole keyboard matrix once into eight bytes $9DE2, then asks about one key at a time by its number in the matrix, row times eight plus column $B476. The five controls sit together in a table of key numbers $B4BC.

Next to the game's own messages sits a page of text that starts with 22,7, the BBC Micro's command for its teletext mode, and uses teletext colour and double-height codes $B9DD. The page names the BBC keys: CAPS LOCK and CTRL to rotate, COPY and DELETE to freeze, ESCAPE to quit. A routine prints the page through the C64's own character output and waits for Space $B74B, but nothing in the code traced so far calls it. The crackers added a line at the bottom: "Cracked By The Syndicate For TCI !".

02 · Loading

Two unpackers before the first instruction

This copy is a crack: one packed file, with the title picture shown while it waits for fire on joystick port 1. A second unpacker then rebuilds the game, a short routine moves 61 pages of it up to $8280, and the game's own code starts at $B675 $B675. Its first job is to copy three pages of start-up code to $0400 and run them there $B70B, which is why that code sits at $B773 in memory but is written for $0400 $B773.

Once running, the game has one interrupt handler $8943. It splits the screen by working down a list of raster lines, each naming one of five handlers $8964, so the status bar at the top and the cave below get their own settings.

03 · Screens

From the title to the first planet

Title. The loading picture, signed "Bob". This crack adds "TCI" under the name.

Attract mode. A demo pilot flies level 1 and carries the pod away. Space starts a game.

Arrival. Each ship appears out of a yellow cross.

Level 1. The fuel tank, a gun, the pod on its stand, and the reactor on the right. Fuel, lives in reserve, and score run along the top.

Shield. Space turns the ship into a green circle and burns fuel faster than thrust.

High scores. The table between games. In this copy every entry reads SYNDICATE.