Datasheet

Table Of Contents

Product data sheet

COMPANY PUBLIC

Rev. 3.6 — 28 November 2017

115436 31 of 222

NXP Semiconductors

PN532/C1

Near Field Communication (NFC) controller

8.1.8 Debug UART

The Debug UART is implemented to assist debug using UART_RX and UART_TX pins.

8.1.8.1 Feature list

The Debug UART has the following characteristics:

• Full duplex serial port

• Receive buffer to allow reception of a second byte while the first byte is being read out

by the CPU

• Four modes of operation which support 8-bit and 9-bit data transfer at various baud

rates

• Supports multi-processor communication

• Baud rate can be controlled through Timer1 or Timer2 baud rate generator

8.1.8.2 Debug UART functional description

The serial port has a receive buffer: a second byte can be stored while the previous one is

read out of the buffer by the CPU. However, if the first byte has still not been read by the

time reception of the second byte is complete, one of the bytes will be lost.

The receive and transmit data registers of the serial port are both accessed by firmware

via the Special Function Register S0BUF. Writing to S0BUF loads the transmit register;

reading from S0BUF accesses a physically separate receive register.

The serial port can operate in 4 modes. These modes are selected by programming bits

SM0 and SM1 in S0CON:

• Mode 0:

– Serial data are received and transmitted through UART_RX. UART_TX outputs the

shift clock. 8 bits are transmitted/received (LSB first)

Baud rate: fixed at 1/6 of the frequency of the CPU clock

• Mode 1:

– 10 bits are transmitted through UART_TX or received through UART_RX: a start

bit (0), 8 data bits (LSB first), and a stop bit (1)

– Receive: The received stop bit is stored into bit RB8 of register S0CON

– Baud rate: variable (depends on overflow of Timer1 or Timer2)

• Mode 2:

– 11 bits are transmitted through UART_TX or received through UART_RX: start bit

(0), 8 data bits (LSB first), a 9th data bit, and a stop bit (1)

– Transmit: the 9th data bit is taken from bit TB8 of S0CON. For example, the parity

bit could be loaded into TB8.

– Receive: the 9th data bit is stored into RB8 of S0CON, while the stop bit is ignored

– Baud rate: programmable to either 1/16 or 1/32 the frequency of the CPU clock