zx spectrum

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ZX Spectrum System Tour: Text Mode – Bumbershoot Software
2 months ago
- Sinclair BASIC can coexist with machine code via SAVE/LOAD with CODE, CLEAR to reserve memory, and USR function to call routines.
- The Z80 memory map on 48K Spectrum: ROM at $0000-$3FFF, graphics RAM at $4000-$5AFF, and the rest is RAM; IY register points to system variables at $5C3A and must not be modified.
- Text output uses RST $10 to print characters; control codes $10-$17 replicate BASIC text commands (INK, PAPER, etc.) and AT takes two arguments.
- User-defined graphics (UDG) are stored at the address pointed by IY+65; you can load custom character data (8 bytes each) into that area.
- System variables ATTR-T, MASK-T, ATTR-P, MASK-P, and P-FLAGS control text attributes; the ROM routine CLS at $0D6B clears the screen and resets temporary colors.
- Keyboard input can be read via interrupt-driven scanning (LAST-K, FLAGS) or direct I/O port reading; joystick reading uses port $1F for Kempston.
- A complete example program demonstrates clearing the screen, loading custom graphics, printing formatted text, and waiting for a keypress, producing a smaller binary than the BASIC equivalent.
ZX Spectrum System Tour: Sound
2 months ago
- The ZX Spectrum offers two sound options: a 1-bit beeper and an AY-3-8910 synthesizer chip.
- The 1-bit beeper can be controlled via BIOS routine at $03B5 using frequency and duration codes derived from formulas.
- A direct beeper routine with precise timing avoids branch timing issues using JP instructions instead of JR.
- The direct beeper method suffers from CPU wait states due to video memory access, requiring code relocation or workarounds.
- The AY-3-8910 chip on Spectrum 128 is programmed via ports $FFFD and $BFFD with a clock of 3.5469 MHz.
- The beeper is best for short sound effects, while the AY-3 chip can handle more complex music and ambient sounds.
Finishing the ZX Spectrum Shooting Gallery
2 months ago
- Porting Shooting Gallery to ZX Spectrum, focusing on shot mechanics including data structures, movement, deletion, spawning, display lists, rendering, and collision detection.
- Designed data using structure-of-arrays: max_shot_y, shot_y (16), shot_x (16), shot_collide (16), num_shots, shot_tails, and shot_heads arrays.
- Autonomous movement updates shot Y coordinates by subtracting 2 each frame; shots at Y=0 are retired.
- Retiring shots uses a compacting scan with IX register to copy non-deleted entries, updating max_shot_y and reducing array size.
- Spawning new shots checks constraints (shot_requested, max_shot_y<124, num_shots<16) then sets Y=146, X based on blaster_x with facing adjustment.
- record_display_list generates shot_tails (erase locations) and shot_heads (draw addresses, masks, indices) from shot arrays, handling collisions and off-screen shots.
- Rendering: erase_shot_tails clears bytes at stored addresses; draw_shots composites pixels using OR and detects collisions via AND with screen memory, updating shot_collide.
- Main game loop order: halt, erase targets and shot tails, draw targets, update blaster, draw shots, handle input, move autonomous, compact shots, new shot, record display list.
- Efficiency measurement using border color shows solid 50 FPS; spikes occur only when hitting targets due to score header redraw.
- Project concluded as most involved port; lessons learned on Z80 instruction selection and using IX for structure-of-arrays, but overall successful and fast enough.

zx spectrum

ZX Spectrum System Tour: Text Mode – Bumbershoot Software

ZX Spectrum System Tour: Sound

Finishing the ZX Spectrum Shooting Gallery