KC87 tape loading tone should be silent on internal speaker

[coignard]

Hi @floooh,

I studied how the KC87 speaker circuit works and noticed a discrepancy. Bit 7 of system PIO port A ("Lautsprecher-Piep") gates the internal speaker. During tape operations the OS keeps this bit cleared, so the CTC channel 0 tone should go to the cassette output only, not the speaker. The hardware manual recommends using a recorder with Mithörkontrolle for tape monitoring, which implies the KC87 does not route this signal through the internal speaker at all.

The chips emulation appears to drive the speaker directly from ZCTO0 without applying the bit 7 gate, so the tone is audible when it should not be.

René Coignard

[floooh]

Yes, very likely that I got that wrong. The KC87/Z9001 and Z1013 are at best "tier 2" emulations where I didn't care all that much about correctness. It might be a while until I get around tinkering with the emulators though, need to focus on the sokol headers for a while.