I have an idea for stealth PSX on a Messiah 2 system –
Problem is that I don't code, so if someone can write it out I'd be happy to test them. Or if this idea cannot work, please tell me.
Ok, you will need PIC12508 chip
Now, the chip pin will listen to the SCEX line on the Messiah 2 for signal on. Because SCEX is only active if you put the Messiah 2 into PSX mode. So we have an activate line. But the tricky thing here is that the SCEX signal is pulsed and not constant, so that the chip would have to respond to a rather short and quick signal.
Obviously power, ground and then finally the stealth output to the actual SCEX line on the mobo. And there you have it. For 89c, you can have stealth PSX without waiting for the Messiah team to incorporate it.
The Yellow PS2 auto-boots all. PS2, PS1 stealth and DVD movies.