RFID read write doc

ManualsBrandsParallax ManualsRFIDSerial RFID Reader / Writer Module

Error Checking

The RFID Read/Write Module responds to each command with a single-byte status/error code in

hexadecimal format followed by any returned data, if applicable. In most standard implementations, the

user will repeatedly call the desired function until the ERR_OK status byte is returned, indicating that the

function successfully completed with no errors.

For scenarios where more error checking is desired, the RFID Read/Write Module provides detailed error

code values:

Tag Details

The RFID Read/Write Module works exclusively with the EM Microelectronics-Marin SA EM4x50 1kbit

R/W transponder tags at 125kHz. A variety of different tag types and styles exist with the most popular

ones made available from Parallax.

The memory map and corresponding address locations for the EM4x50 tag are shown below. Each

address holds a 32-bit (4 byte) value.

The User Data Area can be optionally secured using a 32-bit password to allow only authorized read and

write operations. This password is stored in

ADDR_Password

and can be changed by the user via the

RFID_SetPass command with knowledge of the current password. For security reasons, it cannot be read.

As such, if your tag is password-protected and you forget the tag’s password, you will be unable to

retrieve the contents of the User Data Area.

ADDR_Protect

and

ADDR_Control

are modified directly by the RFID Read/Write Module and, in normal

scenarios, should not be changed by the user.

Value Name Description

0x01 ERR_OK No Errors

0x02 ERR_LIW Could not find a Listen Window (LIW) from the tag

0x03 ERR_NAK

Received a No Acknowledge (NAK), possible communication error or

invalid command/data

0x04 ERR_NAK_OLDPW

Received a No Acknowledge (NAK) sending the current password during

the RFID SetPass command, possible incorrect password

0x05 ERR_NAK_NEWPW

Received a No Acknowledge (NAK) sending the new password during the

RFID SetPass command

0x06 ERR_LIW_NEWPW

Could not find a Listen Window (LIW) from the tag after setting the new

password during the RFID SetPass command

0x07 ERR_PARITY Parity error when reading data from the tag

Address (decimal) Register Description

0 ADDR_Password Password (not readable)

1 ADDR_Protect Protection word

2 ADDR_Control Control word

3-31 User Data Area Non-volatile EEPROM storage area for user data (116 bytes)

32 ADDR_Serial Device serial number (unique, read-only)

33 ADDR_DeviceID Device identification (used to identify tag family, read-only)