AS3909 datasheet(59/77 Pages) AMSCO

59 / 77 page

ams Datasheet, Confidential: 2013-Oct [3-02]

AS3909/AS3910 – 59

Appl icatio n I n f o rm a t i o n

Please note that after getting an interrupt due to a collision, the

reader has to wait for the transponders to finish sending their

messages before sending a new command. The end of

transponder message is indicated by the End of Receive

interrupt. It may also happen that the interrupt due to collision

and due to end of receive are read at the same time (in case

reaction to the first interrupt is slow and collision happens at

the end of transponder message). Collision Register (#0A) can

be read after receiving collision interrupt while the FIFO can

only be read after receiving the End of Receive interrupt.

There is also a slight possibility that the end of message flag is

just written to the Interrupt Register while it is being erased at

the end of the Interrupt Register read due to the collision

interrupt. In such a case there is no end of receive interrupt. In

case it is not clear whether the receive logic is still processing

response the Active Receive bit (rx_act) in FIFO Status Register

can be consulted (See “ISO-14443B, Reduction of TR0 and TR1

and Suppression of EOF/SOF in PICC Response” on page 67 for

details about Active Receive bit).

SELECT

The SELECT command uses standard frame, response to the

SELECT command (SAK) contains also a CRC, so before sending

this command the configuration bit crc_rx of Configuration

contains CRC the direct command Transmit with CRC can be

used.

Receiving 4-Bit Tag Response Frame

Mifare Ultralight tag uses 4 bit response frame to indicate ACK

and NACK. The AS3909/10 framing expects that response frame

is composed of bytes (except in case of anticollision frame) and

it rejects a 4 bit response frame as an error (error due to receive

data coding). By setting the bit 1 (frm4l) of register #0B, a 4 bit

response frame is correctly processed and put in FIFO (MSB bits

of first byte). In case of setting this bit a standard frame response

is not processed correctly.

Response to Mifare Ultralight WRITE command is either ACK or

NACK. So in case of this command bit frm4 has to be set to

distinguish between the two possible 4 bit responses.

Response to READ command is either a standard frame, in case

command is correctly processed, or a NACK, in case of an error.

In this case the bit frm4 can not be used, interrupt due to receive

data coding error should be interpreted as a NACK.

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