Cheap RFID (125kHz) Reader/Writer from China 
============================================

The reader is labeled :

 * on the front : RF ID Reader
 * on the back : D302 EM Card Encoder MADE IN CHINA
 
This reader / writer should Work with cards :  EM4305 and T5567.

Drivers
-------

After some quick research it appears the reader has a CH341 USB / Serial Chip.
To make it work under OSX the driver must be installed.

Check 
 * http://blog.sengotta.net/signed-mac-os-driver-for-winchiphead-ch340-serial-bridge/
 * https://tzapu.com/making-ch340-ch341-serial-adapters-work-under-el-capitan-os-x/
 
Once driver are installed, the RFID reader can be accessed with the following parameters : 
 * Speed : 4800 bauds
 * Bits : 8
 * Parity : none
 * Stop : 1

Initialline states 
 * DTR Off
 * RTS Off

Take care to wait some time ~ 500ms after opening serial port before sending any command. If the command is sent too early the reader discard it. 
 
Protocol
--------

After some quick investigations, it appears the commands look like the following scheme : 

```
02 | NN NN | LL | PP .. PP | CC | 03
```

 * 02 : start byte
 * NN NN : command to execute
 * LL : payload length
 * PP .. PP : payload if needed
 * CC : checksum  02 ^ NN ^ NN ^ LL ^ PP ... ^ PP = CC (all bytes including the start one are xor'ed to compute the checksum)
 * 03 : stop byte
 
Commands
--------

CMD 01 00 : **HELLO / ACK**

```
-> 02 01 00 00 03 03 [send hello to the reader]
<- 02 01 00 00 03 03 [recv acknowledge from the reader]
```

CMD 01 a4 : **READ**

```
-> 02 01 a4 0b 00 00 00 00 00 00 00 00 00 00 00 ac 03 [send read card]
<- 02 01 00 05 XX XX XX XX XX CC O3 [recv card number XX XX XX XX XX with checksum CC]
```

CMD 01 a5 : **WRITE**

WP can be 0x00 (Read / Write) or 0xff (Read only). Once Write protect byte has been set, the card cannot be updated anymore
```
-> 02 01 a5 0b 00 00 00 00 00 WP XX XX XX XX XX CC 03 [send write card number XX XX XX XX XX with checksum CC]
<- 02 01 00 00 03 03 [recv acknowledge from the reader]
```


// TODO : check errors codes, ...