AS3911B datasheet(30/155 Pages) AMSCO

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AS3911B – 30

ams Datasheet: 2014-Jun-12 [v1-08]

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

Mask Receive Timer and No-response Timer

Mask Receive Timer and No-response Timer are both

automatically started at the end of transmission (at the end of

EOF).

Mask Receive Timer

The Mask Receive Timer is blocking the Receiver and reception

process in framing logic by keeping the rx_on signal low after

the end of Tx during the time the tag reply is not expected.

While the Mask Receive timer is running, the Squelch is

automatically turned on (if enabled). Mask receive timer does

not produce an IRQ.

The Mask Receive Timer timeout is configured in the Mask

Receive Timer Register.

In the NFCIP-1 active communication mode the Mask receive

timer is started when the peer NFC device (a device with which

communication is going on) switches on its field.

The Mask Receive timer has a special use in the low power Initial

NFC Target Mode. After the initiator field has been detected the

controller turns on the oscillator, regulator and receiver. Mask

Receive timer is started by sending direct command Start

Mask-receive Timer. After the Mask Receive Timer expires the

receiver output starts to be observed to detect start of the

initiator message. In this mode the Mask Receive Timer clock is

additionally divided by eight it (one count is 512/fc) to cover

range up to ~9.6 ms.

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 (4.72 μs), which covers range up

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

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

AS3911B Datasheet(PDF) 30 Page - ams AG

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