update README with PCD usage example and functionalities

Author: georgesFoundation

README.md

@@ -9,19 +9,82 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 Rust library to manipulate ISO/IEC 14443 data.
 
-## Fontionalities
+## Functionalities
 
 - [x] Type-A
     - [x] iso14443-3: REQA/WUPA/ATQA/ANTICOLLISION/SELECT/SAK/HLTA
-    - [x] CRC_A checks
+    - [x] iso14443-3: CRC_A checks (hardware-accelerated or software)
+    - [x] iso14443-3: PCD activation with anticollision cascade (4/7/10-byte UIDs)
     - [x] iso14443-4: RATS/ATS/PPS
     - [x] iso14443-4: PCB (Protocol Control Byte)
     - [x] iso14443-4: Block format (I-block, R-block, S-block)
-    - [x] iso14443-4: Block chaining
-    - [x] iso14443-4: Protocol state machine
+    - [x] iso14443-4: PCD transport layer (APDU exchange, chaining, WTX, error recovery, DESELECT)
+    - [x] iso14443-4: Generic block protocol handler (reusable for PCD and PICC)
 - [ ] Type-B
 
-## Example Usage
+## Usage
+
+```rust
+use iso14443::type_a::{
+    activation::{activate, ActivationError},
+    pcd::{Pcd, PcdError},
+    vec::FrameVec,
+    Cid, Frame, Fsdi, PcdTransceiver,
+};
+
+/// Dummy PCD transceiver — replace with your real hardware driver
+/// (e.g. SPI to an NXP PN532 or ST25R3916).
+struct MyTransceiver;
+
+#[derive(Debug)]
+struct MyError;
+
+impl PcdTransceiver for MyTransceiver {
+    type Error = MyError;
+
+    fn transceive(&mut self, _frame: &Frame) -> Result<FrameVec, MyError> {
+        // Send frame bytes over SPI/I2C/UART, return the PICC response.
+        todo!("implement for your hardware")
+    }
+
+    fn enable_hw_crc(&mut self) -> Result<(), MyError> {
+        // Enable hardware CRC if the chip supports it.
+        // Return Err to fall back to software CRC.
+        Err(MyError)
+    }
+}
+
+fn talk_to_card(t: &mut MyTransceiver) -> Result<(), Box<dyn std::error::Error>> {
+    // ISO14443-3A: detect tag, resolve UID
+    let activation = activate(t).map_err(|e| format!("{e:?}"))?;
+    println!("UID: {:02x?}", activation.uid.as_slice());
+
+    // Only proceed to ISO14443-4 if the tag supports it
+    if !activation.sak.iso14443_4_compliant {
+        println!("Tag does not support ISO14443-4");
+        return Ok(());
+    }
+
+    // ISO14443-4: RATS/ATS negotiation, open a session
+    let cid = Cid::new(0).unwrap();
+    let (mut pcd, ats) = Pcd::connect(t, Fsdi::Fsd256, cid)
+        .map_err(|e| format!("{e:?}"))?;
+    println!("ATS: {ats:?}");
+
+    // Exchange an APDU (e.g. SELECT application)
+    let select_apdu = [0x00, 0xA4, 0x04, 0x00, 0x07,
+        0xD2, 0x76, 0x00, 0x00, 0x85, 0x01, 0x01, 0x00];
+    let response = pcd.exchange(&select_apdu)
+        .map_err(|e| format!("{e:?}"))?;
+    println!("Response: {:02x?}", response.as_slice());
+
+    // Clean up
+    pcd.deselect().map_err(|e| format!("{e:?}"))?;
+    Ok(())
+}
+```
+
+## CLI Parser
 
 An example is provided to parse raw data from the ISO14443 protocol: