6

In the Spectrum lexicon, a t-state is just a "time state" — a single cycle of the ~3.5Mhz clock. For implied evidence of that, see e.g. this document of 128K ZX Spectrum Technical Information, which states ... there are 70908 T states per frame, and the '50 Hz' interrupt occurs at 50.01 Hz. 70908 t-states per frame * 50.01 Hz = 3.546 million t-states ...


5

DAC is a digital analog converter. There is no such periphery on C64, but the closest to it is the SID chip, for playing sound. Also the SID chip was not designed for that. It can play ADSR (attack-decay-sustain-release) sounds with 4 pre-configured waveforms: This can be hacked to work like a DAC. It can only 16 signal levels, but it is enough to produce ...


2

The mysterious "T" is CPU clock tick, as mentioned above, and it figures as a "non-dividable time quantum" on this computer. When you need to do something with perfect timing (e.g. audio generation), you had to compute how much ticks your routine takes (each instruction takes a known amount of T). It is very painful, but because ZX Spectrum has no HW timers, ...


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