Datasheet

Table Of Contents

Product data sheet

COMPANY PUBLIC

Rev. 3.6 — 28 November 2017

115436 75 of 222

NXP Semiconductors

PN532/C1

Near Field Communication (NFC) controller

8.3.4.1 Mode of operation

The HSU supports only one operational mode, which has the following characteristics:

• Start bit:

– Start bit is detected when a logic 0 is asserted on the HSU_RX line.

• 8 data bits:

– The data bits are sent or received LSB first.

• Stop bit:

– During reception, the Stop bit(s) is detected when all the data bits are received and

when Stop bit(s) is sampled to logic 1. The number of Stop bits is programmable. It

can be 1 or 2.

– During Transmission, after the complete data bit transmission, a variable number

of Stop bit(s) is transmitted. This number is programmable from 1 to 4.

8.3.4.2 HSU Baud rate generator

To reach the high speed transfer rate, the HSU has it own baud rate generator. The baud

rate generator comprises a prescaler and a counter. The prescaler is located before the

counter. The purpose of the prescaler is to divide the frequency of the count signal to

enlarge the range of the counter (at the cost of a lower resolution). The division factor of

the prescaler is equal to 2 to the power HSU_PRE[8:0] (Table 113 on page 77

), resulting

in division factors ranging from 1 (20) to 256 (28). The combination of these 2 blocks

defines the bit duration and the bit sampling.

8.3.4.3 HSU preamble filter

Received characters are sent to the FIFO manager after three consecutive characters

have been received: 00 00 FF. When the frame is finished, and before a new frame

arrives, firmware shall write a logic 1 in the start_frame bit of the HSU_CTR register to

re-activate the preamble filter. If firmware does not write a logic 1 then all characters of the

frame are sent to the FIFO manager (including the preamble).