write.py

#!/usr/bin/env python
import RPi.GPIO as GPIO
import MFRC522

# Keys
DEFAULT_KEY = [0xFF,0xFF,0xFF,0xFF,0xFF,0xFF]

# Selecting key
KEY = DEFAULT_KEY

def format_uid(uid):
    s = ""
    for i in range(0, len(uid)):
        s += "%x" % uid[i]
    return s.upper()

RFID = MFRC522.MFRC522()

print "# RFID Writer\n"
print "Info: Leave the sector field empty to exit.\n"

# Get tag size if available
(status, TagSize) = RFID.Request(RFID.PICC_REQIDL)

while True:
    if TagSize > 0:
        message = "Sector [1 - %s]: " % (TagSize - 1)
    else:
        message = "Sector: "

    try:
        Sector = input(message)
    except:
        print ""
        break
    else:
        if TagSize > 0:
            if Sector >= 32:
                MaxChars = 16 * 15
            else:
                MaxChars = 16 * 3
            message = "Data [max %s chars]: " % MaxChars
        else:
            message = "Data: "
        try:
            text = raw_input(message)
        except:
            print "\n"
            continue
        else:
            print "Waiting for Tag...\n"

    while True:
        (status, TagSize) = RFID.Request(RFID.PICC_REQIDL)

        if status != RFID.MI_OK:
            continue

        if Sector < 1 or Sector > (TagSize - 1):
            print "Sector out of range (1 - %s)\n" % (TagSize - 1)
            break

        # Selecting blocks
        BaseBlockLength = 4
        if Sector < 32:
            BlockLength = BaseBlockLength
            StartAddr = Sector * BlockLength
        else:
            BlockLength = 16
            StartAddr = 32 * BaseBlockLength + (Sector - 32) * BlockLength

        BlockAddrs = []
        for i in range(0, (BlockLength - 1)):
            BlockAddrs.append((StartAddr + i))
        TrailerBlockAddr = (StartAddr + (BlockLength - 1))

        # Initializing tag
        (Status, UID) = RFID.Anticoll()

        if Status != RFID.MI_OK:
            break

        # Writing data
        RFID.SelectTag(UID)
        status = RFID.Auth(RFID.PICC_AUTHENT1A, TrailerBlockAddr, KEY, UID)
        if status == RFID.MI_OK:
            data = bytearray()
            data.extend(bytearray(text.ljust(len(BlockAddrs) * 16)))
            i = 0
            for block_num in BlockAddrs:
                RFID.Write(block_num, data[(i*16):(i+1)*16])
                i += 1
            print "UID:  ", format_uid(UID)
            print "Data: ", text[0:(len(BlockAddrs) * 16)], "\n"
        else:
            print "Can't access sector", Sector, "!\n"
        RFID.StopCrypto1()
        break

RFID.AntennaOff()
GPIO.cleanup()