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misc/cvs.cpp: Add documentation in comments about the effects of the sound registers observed by poking values on a real CVS PCB. (#13099)

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Paul Swan 2024-12-18 19:46:09 -08:00 committed by GitHub
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src/mame/misc/cvs.cpp
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@ -682,6 +682,25 @@ void cvs_state::sh_trigger_w(offs_t offset, u8 data)
// offset 2 is used in darkwar, spacefrt, 8ball, dazzler, superbik, raiders
// offset 3 is used in cosmos, darkwar, superbik, raiders
/**********
Additional notes from poking the CVS sound hardware with an
In Circuit Emulator from PrSwan (Paul Swan).
I have recordings available.
- 0x1884 - Enables an XP8038 frequency generator IC
Reflected on pin 10 of a 4016.
The frequency is set by 0x1840, the 8 bit DAC register.
Not all 0x1840 values were tested, but:
0x00 - off, 0x1884 enable has no sound.
0x55,0xAA,0xFF - increasing value has higher frequency
- 0x1885 - A scope showed this halving the XP8038 amplitude with a little decay.
Causes 4016 pin 11 to rise (on) and decay-fall (off)
- 0x1886 - Mikes comment above about a high pitched whistle didn't match my PCBs. His was faulty?
Outputs a complete Galaxia-style ship fire sound, with attack-to-on and decay-to-off.
- 0x1887 - Reflected on an LM380.
Causes an envelope-like operation on the XP8038 tone with attack (on) and decay (off).
***********/
data &= 1;
if (data != m_sh_trigger[offset])