So, I am interested in the PSIO, it would be nice to not have to switch disks physically to load different games, but the thing is, the PSIO requires you to solder a special chip as well as cut some traces on the PS1 in order to work. Does anyone know if this will interfere with a modchip or or the modchip would interfere with the PSIO and/or it's board that you need to solder on?
They don't interfere with each other. You can install PSIO either with or without a modchip in the console. Note that PSIO doesn't care about disc region anyway, so if you are running disc images from the SD card they can be from any territory and will still boot no matter if you have a modchip or not. Either unplugging the PSIO cartridge completely or using the "Boot CD" option in PSIO uses the original CD controller and drive and will only boot in-region originals unless you have a modchip.
That's another thing that I was wondering about. They mentioned that the reason for the Switchboard was that it re-routes some signals from the CD drive to the PSIO itself, and that this only happens while the PSIO is plugged in. Does this Switch Board somehow know when a PSIO is connected over something else (Although I understand it's very simple in design) or would it also go off if I were to plug something else into the parallel port like a Game Shark?
It's worked with everything I've tried including various cheat carts, a Video CD card, MP3 player, etc. The signal used to control the switch board is also wired to a pin that's normally connected to ground in the console, so I can't really think of any reason that anything except a PSIO would even try to pull it high.
Reviving this thread! I also have doubts about this. Even if the PSIO doesn't care about the modchip, that doesn't mean the modchip doesn't care about PSIO (in terms of what the modchip does). The way the modchip works (at least stealth ones) is that, when the disc is in 1x mode (Audio mode, that's where check the presence of the SCEx string) it starts nuking the hardware with the string the console is looking for, until the drive moves to a higher speed. Since PSIO it's basically an ODE (that's what the switch board does, map the optical disc data lines to PSIO), even if the PSIO is able to send those strings and override PS1's security, those strings would be send by PSIO and the modchip itself (because the modchip is seeing just a regular disc, being emulated by PSIO). Note that this would also apply if you're playing an original disc, the modchip would still be sending the string. A solution for overriding the modchip, at least at first glance, is to use a pnp / npn transistor attached to the 3.3v / ground of the modchip and the switch board, in order to cut the modchip's power when PSIO is connected. That way we avoid sending redundant SCEx strings to our consoles, provided both by PSIO and the modchip. (I'm not being specific about this because I don't have a PSIO in my hands in order to do it). Note: The modification I'm saying it's probably not needed at all, but I'm kinda paranoic, and because of that, I don't want for the modchip to be enabled if we don't need it. If someone could correct me if I'm wrong, that would be great!
I am pretty sure it is not a problem because PSIO replaces the CD-ROM MCU. Since that part is replaced, there is no copy-protection. What they seem to do, is to use the PIO address and data lines to emulate the CD-ROM MCU. Things like the interrupts must remain the same, which would explain the small hardware mod that is still required. I remember that the memory range for the real CD-ROM MCU cannot be moved elsewhere on the PS, so part of the mod is to disable the chip select signal to it. But I never got a set, so I don't know for sure which lines are involved in the hardware mod.
Simple answer is "usually the modchip would be ok, but it may depends on the design of the specific modchip".I have used 2 switch board modded PS1, SCPH-7501 and 5500, they all have early 5-lines modchip installed. And they work fine with PSIO. I have test them with genuine PS1 disc that not in the region of those console and they can be boot flawlessly though CD Boot feature in PSIO menu. So I think the modchip is working, at least for region bypass. But I have no burnt CD in hand, so I'm not completely sure if backup CD woluld be working. By referencing the official scheme graph: If a PSIO is plugged in, EN(CART IN) is pulled high.Then the A-B connection is enabled for U1B and U1C, but disabled for U1A nor U1D. So PI(PSIO interrupt) would be connected to CI(CPU interrupt) and XI(CD interrupt) would be disconnected, XE(CD_CS, chip select?) would be disconnected from CE(CPU_CS) also.
When you select the "boot CD" option, PSIO drives the EN pin low to restore access to the internal CD-ROM controller and asserts reset. At that point, the console acts in exactly the same way it would if PSIO wasn't installed, and the overall behavior comes down entirely to the modchip installed (if any). When PSIO is plugged in the CD interface chip (CXX1815, etc.) on the main board is disabled and all the accesses to it are routed to the FPGA on the PSIO board. This also effectively disables the original mechacon MCU and the CD DSP, since the only way they can be accessed is via the CD interface chip. The net result of this is that although any mod chip installed may be sending SCEx strings to the mechacon it doesn't matter, since the R3K can't communicate with it and always gets the simulated drive status information from PSIO.
