Capture data on a pcb data line?

[bozza]

Hopefully this is the right place to ask.
I am fascinated by early console modchips and I am wondering how they were developed.

One of the first points of entry for the chip developers must have been to capture some data from either a running console or a console that was turned off.

I have glanced over flash chips and how those can be read by attaching wires to the pcb or directly to the flash chip. Reading can be done over a bunch of different interfaces for example sdio, spi, jtag and perhaps some others.
Locating a serial interface can be another point of entry.

What do you do if you have no idea what kind of communications are going through the pcb because it is unlabeled and the flash chips are hidden under or inside the cpu for example? Sometimes they use undocumented chips too. If you have a nand controller or a flash chip that is undocumented how do you find out which pin is the data line, clock, cmd and whatever else there is?

The first PlayStation is interesting as the modchip is quite simple in theory. There is a wobbly line on the CD which cannot be reproduced by a CD burner. The line encodes 4 letters. When the console boots a disc it first reads this wobbly line. If it is present the boot process continues. If else the console locks up. What the modchip does is send these 4 letters to the cpu to emulate the wobbly line being read by the disc reader. The modchip probably sits somewhere between the disc reader and the cpu in the circuit. There is an open source version of a ps1 modchip out there.

How would have the developer gone to identify the signal and how it is passed around on the pcb in the first place?

I would appreciate any answers or insights at all.

Thank you in advance

[perieanuo]

hi,
https://www.saleae.com/home2/
just kiddin, there are tons of logic analyzers on the market, depends on number of data lines needed, speed, comm protocol