Testing your MM3 pins, pin 6 is the data, pin 2 NOT LED

General information to do with the PlayStation 1 Hardware. Including modchips, pinouts, rare or obscure development equipment, etc.
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Testing your MM3 pins, pin 6 is the data, pin 2 NOT LED

Post by leafy » September 10th, 2020, 5:53 pm

First, this is about the Multimode 3 mod chip. I think in most cases PSNee would be better, but many people still have or burn the MM3. MM3 is compiled for the PIC12C508, but can be written to the PIC12F508. You can't slap it on other chips without recompiling the source, and nobody is coughing it up.

The rumor was that pin 2 was for an optional LED. This seems odd because to see the serial data activity you would just use pin 6 where the action is going on. Old diagrams for Multimode 2 indeed show an LED on pin 2. At some point whatever was going on with pin 2 was removed from the source code.

I have a SCPH-9001 with wires leading to the space under the door open button. I have a socket for a DIP, so I can try different 8 pin chips if I want. So, I removed my MM3 (that I burned) and attached wires to the socket and extended these leads out of the vent. I attached them to a solderless breadboard and installed the chip so I could more easily test the signals and also see a game load (or not).

I found that in some cases using the meter on the pins of the chip caused interference and the game would not boot. Mostly it worked fine. MM3 is has a bunch of modes when you hit reset. They might be dino modes like on 2.8a.

The activity of clocking out the datagrams seems to be going on at pin 6 as was described to me.

On an analog meter, on the AC voltage scale (0-10 V AC), I can see the voltage bounce between about 1 and 2 volts, and an LED wired from pin 6 to frame ground blinks also.

The other pins mostly stay high around 4 volts (aside from pin 1 and pin 8 which are Vcc and Vss not GPIO).
1. VCC
2. An optional activity LED output.
3. Used to support stealth mode for anti modchip games.
4. Reset button input.
6. Data output to send the correct copy protection serial message so the console accepts the disc.
7. CD door input.
8. GND
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Post by daifuku74 » January 16th, 2022, 11:22 pm

Hello leafy and thanks for your input on this subject.
Practical information about this LED mod on the internet is both scarce and different from source to source.

I installed the MM3 chip and a common cathode LED and confirm your install is working great. :dance

So, if I understand correctly, the blinking of the LED indicates when the modchip sends data to the console (bypass region lock etc), am I correct?

Just to be sure to make the difference with LED activity when the lens is reading data.
Thanks a lot.

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Post by leafy » February 1st, 2022, 4:36 pm

Correct, pin 6 on MM3 is the pin that sends out the SCEA, SCEI, and SCEE datagrams to fool the PSX BIOS when you use either a burned disk or disk from another region.

So, yes, if you attach an LED you can visualize this activity... as long as the LED doesn't use too much current and there is enough left for the signal to the PSX.

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