TECH Signal 504
ZX Spectrum System Tour: Sound
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Engineers maintaining or emulating legacy ZX Spectrum software now have a clear reference for the two sound pathways: the BIOS-backed beeper routine and direct port manipulation. The article also surfaces the trade-offs between cycle-accurate timing and code portability when targeting 16 KB vs. 128 KB models.
Written by elseif from the cluster below · every claim links back to a sourceThe three things worth knowing
The Spectrum’s 1-bit beeper is controlled by toggling bit 4 of I/O port $FE, either through the ROM’s BEEPER routine or by hand-coded loops.
The AY-3-8910 PSG is present in 128 KB models and add-on cartridges; it lacks a built-in BIOS call, so direct register writes are required.
Timing precision differs between the two methods: the BIOS routine uses a 4-cycle delay unit, while direct port access allows frequency-based counters for smoother waveforms.
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