Memory card with seven-segment display

[reachC]

Hi! I found some strange memory card in the dumpster a while ago.
When I start the PlayStation the display always shows "AJ" and then goes off after a few seconds.
Does anybody know what exactly this is?

[rama3]

Sure.
It's a multi slot Memory Card. You control it by holding Select and L1 or R1. Each slot then shows up as a single card.
Beware though that they're a little unstable. Never try to format them, or do any operations using a manager other than the PSX BIOS one. Otherwise, they tend to corrupt and take all your saves with them.

[reachC]

Thanks rama3! Works perfect!

[Orion_]

I have a memory card like this but with a physical button on the memory card to switch bank.
How is it possible without a physical button ?
I don't understand how this memory card can tell the playstation to trigger something from the gamepad ?
Wouldn't it require some custom code to be injected in memory ?
If this is possible from a memory card, this mean that an hacking method is possible using a simple memory card just like the FreeMcBoot on PS2 ?

[reachC]

Maybe because the controller and the memory card share the same serial connection and the card listens to the controller input?

[rama3]

Yep, these cards just listen in on the bus

[Orion_]

ok, I didn't know the gamepad and memory card bus was shared.
that's kind of messed up ...

[rama3]

Well, it's economical. The bus is fast enough to serve many peripherals, so they could save on controllers and board space + cabling.