What is MISO pin in the RFID Module?

In the Serial Peripheral Interface (SPI) protocol that RFID reader modules such as the MFRC522 use to talk to a microcontroller, every signal line is named strictly from the perspective of the master device: an "In" line carries data arriving at the master, and an "Out" line carries data leaving the master.

Applying this to the RFID module (the SPI slave) and its host microcontroller (the SPI master): on this pin, the slave sends data that the master receives, so the correct, datasheet-defined name is Master In Slave Out.

The other options replace this precise data-direction naming with unrelated or invented phrases:

• Manage Internal Slave Output turns the acronym into an internal management action, but no SPI signal performs internal management; every SPI pin name refers to a data-carrying wire, not a control process.

• Master Internal Search Optimization imports the phrase search optimization from software and algorithms, a concept that has nothing to do with a hardware serial-communication pin.

• Manage Input Slave Op shortens Output to Op and swaps in a generic Input instead of naming a real signal role; no SPI datasheet defines a pin by this label.

Cross-checking with the companion signal confirms the naming rule: MOSI (Master Out, Slave In) is the mirror-image line that carries data the master sends to the slave. Since both names follow the same master-centred convention, only Master In Slave Out is consistent with how SPI signal names are constructed, confirming the saved answer.