zxspectrum

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zxspectrum

by thisismypassword

Cart #zxspectrum-0 | 2023-10-13 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

4

How?

• It's recommended to run it in Pico-8 with "-displays_x 2 -displays_y 2".
• If you don't (say, if you run it in the BBS), you'd have to move the mouse around to see the whole window

• In particular, move the mouse to the bottom-left corner to see the Spectrum prompt

• You can use the keyboard to type stuff
• The symbol key is Tab.
• ZX Spectrum keyboard layout: http://slady.net/Sinclair-ZX-Spectrum-keyboard/layout/
• ZX Spectrum user manual: https://worldofspectrum.org/ZXBasicManual/

• Non-spectrum keys like punctuation/backspace automatically press the right shift/symbol combination

• To load a tape:
• First type 'j' for load.
• Then type double-quotes (") twice. On the BBS or on non-standard keyboard layouts, you're better off pressing Tab+P to get double-quotes. (On BBS, '~' might also work - looks like an emscripten bug).
• Now, press enter.
• Only after that, drag a tape (in .tap or .tzx format) to Pico-8.

• Reset Pico-8 if you want to drag another tape.

• By default, the arrow keys move the cursor. You can instead have them use the Kempston joystick or the Sinclair joysticks in the pause menu.

What?

• It's a ZX Spectrum emulator
• It's quite slow. 2-5 times slower than the real thing.
• I don't know if sound is broken or just too slow to be ok.

• Tapes with copy protection won't work.

• By default, tapes load super-quick if using the loading routines in the ROM. (Can be disabled in pause menu)

• By default, the CPU is underclocked to maintain responsiveness (since pico-8 can't keep up). (Can be disabled in pause menu)

• The included Spectrum ROM is copyrighted by Amstrad, who have allowed its use by emulators.

Wherefore?

• The source code won't bite you if you read it. (But it won't lick you, either)

• Some highlights from the source:
• Using the pico-8 memory for the z80 registers, to get the "16 bit reg = two 8 bit regs" behaviour for free(-ish).
• Using fillp + rectfill to draw each 4x4 block on the screen
• Only drawing modified (or blinking) areas of the vram.
• Pre-calculating the flag results of every single addition and add-with-carry (subtraction is easily derived from that)