037031

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Product data sheet

PUBLIC

Rev. 3.1 — 9 February 2010

037031

7 of 22

NXP Semiconductors

HTRC110

HITAG reader chip

9.7 Serial interface

The communication between the HTRC110 and the microcontroller is done via a three

wire digital interface. The interface is operated by the following signals:

SCLK

clock

DIN

data input

DOUT

data output

SCLK and DIN are realized as Schmitt-Trigger inputs. DOUT is an open drain output with

internal pull-up resistor.

Every communication between HTRC110 and microcontroller begins with an initialization

of the serial interface. The interface initialization condition is a low-to-high transition of the

signal DIN while SCLK is high.

All commands are transmitted to the HTRC110 serial interface starting with Most

Significant Bit (MSB). DIN and DOUT are valid when SCLK is high.

9.8 Glitch filter for increased noise/interference immunity

Connecting pin 5 (MODE) to VDD enables digital filtering of the SCLK and the DIN input

signals. This mode offers improved immunity against glitches on these interface signals. It

is intended to be used in the so called "Active Antenna Applications" where the

microcontroller and the reader communicate via long signal lines (e.g. 1 meter).

In other applications pin 5 (MODE) has to be connected to GND.

Please refer to the HTRC110 application note (Ref. 1) for a detailed description of this

feature.

Fig 4.

Serial signaling