Multi modchips on a single PS2... (Or a way to disable a MOD with no standby mode)
I've made this "thing" to actually disable a Action Mars on a SCPH30000 machine, so I could use the HDD without having to bother with DNAS checkings being compromised by the mod patching. On that PS2 there's only one modchip, but this circuit makes possible the use of two mods at once, which could be interesting for some people.
The circuit is pretty simple. A 74HC4053 (triple 2 to 1 analog channel multiplexer/demultiplexer) is the heart of the "thing" switching the 3 control signals of the connected modchips.
On this circuit, you can think of the 4053 like if it was a A-B switch with 3x3 contacts (3 A-B circuits).
The A point is the signal that flags data communication on the CDVD controller chip. The R point flags a read data operation on the BIOS. The S point is used to send the SCEX signal which causes the PS2 to run a PSX game.Because the R and A points are how the modchip know when it should send the patches, they will renmain blind to what happens on the CDVD chip and bios buses while R and A wires are disconnected . This principle apply for disabling one of the chips or both if the enable signal (H) is not grounded.
R and A inputs shoud get a 10k (103) resistor on each mod to ensure the voltage on the pins will not float, making the chips think there is any access on the bus. The resistors will not affect the operation of the machine.