docs: update mfrc522 reader doc

Author: AlvinSchiller

documentation/developers/rfid/mfrc522_spi.md

@@ -17,27 +17,34 @@ are just routed through to spidev. Have a look at the spidev
 documentation for details if you really want to use a different SPI bus.
 The default setup makes most sense for almost everyone.
 
-### spi_bus *(default=0)*
+### spi_bus *(0)*
 
-The SPI Bus ID. The default bus is 0. For other bus IDs, the RPi also needs to re-configured. For that reason we set this to zero.
+The SPI Bus ID. Fixed to 0, because other bus IDs also need re-configuration of the RPi (refer to RPi documentation).
 
 ### spi_ce *(default=0)*
 
-SPI chip enable pin. On default SPI bus 0, this can be
+The SPI Chip Select (CEx) pin. Mandatory.
 
-- 0 = GPIO8 (Pin 24)
-- 1 = GPIO7 (Pin 26)
+This can be
+- 0 = GPIO8 (SPI0 CE0) - Pin 24
+- 1 = GPIO7 (SPI0 CE1) - Pin 26
 
-For other SPI buses refer to RPi documentation.
+For other SPI buses 
 
-### pin_irq
+### pin_irq *(default=24)*
 
-Mandatory IRQ pin. This can be any GPIO pin.
+The IRQ GPIO pin for card detection. This is an optional pin, but required for interrupt-driven card detection.
 
-### pin_rst *(default=0)*
+If not used,
+- uses pollig mode instead of interrupt event
+- has high CPU usage and may impact system performance!
+- Only use this mode if you have serious interrupt conflicts
 
-Reset pin for hardware reset. This is an optional pin. If not used,
+### pin_rst *(default=25)*
 
+The Reset GPIO pin for hardware reset. This is an optional pin. 
+
+If not used,
 - hardware reset will only be performed by power-on-reset. This has been tested and works fine.
 - you **must** tie the reset pin of the MFRC522 board **high**!
 
@@ -59,14 +66,16 @@ The following pin-out is for the default SPI Bus 0 on Raspberry Pins.
 
 ### MFRC522 default wiring (spi_bus=0, spi_ce=0)
 
-|Pin Board Name  |Function  |RPI GPIO  |RPI Pin  |
-|----------------|----------|----------|---------|
-|SDA             |CE        |GPIO8     |24       |
-|SCK             |SCLK      |GPIO11    |23       |
-|MOSI            |MOSI      |GPIO10    |19       |
-|MISO            |MISO      |GPIO9     |21       |
-|IRQ GND         |IRQ       |GPIO24    |18       |
-|RST 3.3V        |RST       |GPIO25    |22       |
+|MFRC522 Pin Name  |Function            |RPI GPIO          |RPI Pin  |
+|------------------|--------------------|------------------|---------|
+|SDA               |Chip Select (CE)    |GPIO8 (SPI0 CE0)  |24       |
+|SCK               |Serial Clock        |GPIO11 (SPI0 SCLK)|23       |
+|MOSI              |Master Out, Slave In|GPIO10 (SPI0 MOSI)|19       |
+|MISO              |Master In, Slave Out|GPIO9 (SPI0 MISO) |21       |
+|IRQ               |Interrupt Request   |GPIO24            |18       |
+|GND               |Ground              |                  |20       |
+|RST               |Reset               |GPIO25            |22       |
+|3.3V              |Power               |                  |17       |
 
 Some RC522 boards use reversed labeling for MOSI and MISO pins. The good
 thing is, no harm is done to the card reader when incorrectly connected.