AS3911 datasheet(30/149 Pages) AMSCO

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AS3911 – 30

ams Datasheet, Confidential: 2013-Oct [2-03]

A p pl i c at io n I n f o r m at i o n

No-response Timer

As its name indicates this timer is intended to observe whether

a tag response was detected in a configured time started by

end of transmission. The I_nre flag in the Timer and NFC

Interrupt Register is signaling interrupt events resulting from

this timer timeout.

The No-response Timer is configured by writing two

No-response Timer setting registers: No-response Timer

of the No-response timer are defined by setting bits nrt_emv

and nrt_step in the General Purpose and No-response Timer

Control Register.

Bit nrt_step configures the time step of the No-response Timer.

Two steps are available, 64/fc (4.72μs), which covers range up

to 309ms and 4096/fc, which covers range up to 19.8s.

Bit nrt_emv controls the timer operation mode:

• When this bit is set to 0 (default mode) the IRQ is produced

in case the No-response timer expires before a start of a

tag reply is detected. In the opposite case, when start of

a tag reply is detected before timeout, the timer is

stopped, and no IRQ is produced.

• When this bit is set to 1 the timer unconditionally

produces an IRQ when it expires, it is also not stopped by

direct command Clear. This means that IRQ is independent

of the fact whether or not a tag reply was detected. In case

at the moment of timeout a tag reply is being processed

no other action is taken, in the opposite case, when no tag

response is being processed additionally the signal rx_on

is forced to low to stop receive process.

The No-response Timer can also be started using direct

command Start No-response Timer. The intention of this

command is to extend the No-response timer timeout beyond

the range defined in the No-response Timer control registers.

In case this command is sent while the timer is running, it is

reset and restarted.

In the NFCIP-1 active communication mode the No-response

Timer is automatically started when the transmitter is turned

off after the message has been sent. In case this timer expires

before the peer NFC device (a device with which

communication is going on) switches on its field an interrupt is

sent.

General Purpose Timer

The triggering of the General Purpose Timer is configured by

setting the General Purpose and No-response Timer Control

process (triggering by start of reception, after SOF) or to time

out the PCD to PICC response time (triggered by end of

reception, after EOF). In the NFCIP-1 active communication

mode it is used to timeout the field switching off. In all cases an

IRQ is sent when it expires.

AS3911 Datasheet(PDF) 30 Page - ams AG

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