AS3911 datasheet(29/149 Pages) AMSCO

29 / 149 page

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

AS3911 – 29

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

The oscillator output is also used to drive a clock signal output

pin MCU_CLK), which can be used by the external

microcontroller. The MCU_CLK pin is configured in the IO

Configuration Register 2.

Timers

The AS3911 contains several timers which eliminate the need

to run counters in the controller, thus reducing the effort of the

controller code implementation and improve portability of

code to different controllers.

Every timer has one or more associated configuration registers

in which the timeout duration and different operating modes

are defined. These configuration registers have to be set while

the corresponding timer is not running. Any modification of

timer configuration while the timer is active may result in

unpredictable behavior.

All timers except the Wake-up timer are stopped by direct

command Clear.

Exception: In case bit nrt_emv in the General Purpose and

No-response Timer Control Register is set to one, the

No-response timer is not stopped.

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 ~9.6ms.

AS3911 Datasheet(PDF) 29 Page - ams AG

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