SN32F760 Series
32-Bit Cortex-M0 Micro-Controller
SONiX TECHNOLOGY CO., LTD
Page 162
Version 2.0
Clock
bit0
Start
Parity
UTXD
bit1
bit2
bit3
bit4
bit5
bit6
bit7
NACK
2 Stop bits
Extra guard
bit0
Start
…...
Next transfer or First retry
The smart card must be set up with the following considerations:
1.
register so that the USART is not continuously reset.
2.
Program USARTnPRE bits in
register for an initial USART frequency of 3.58 MHz.
3.
If necessary, program the USARTn_DLM and USARTn_DLL to 00 and 01 respectively, to pass the USART clock
through without division.
4.
Program the
register for 8-bit characters, parity enabled, even parity.
5.
register to enable the smart card feature with the desired options, and HW enables
a USART TXD function automatically.
6.
Set up one or more timer(s) to provide timing as needed for ISO-7816 startup.
7.
Program USARTnCLKEN bit in
register to enable the USART clock.
Thereafter, SW should monitor card insertion, handle activation, wait for answer to reset as described in ISO7816-3.
14.10 SYNCHRONOUS MODE
The synchronous mode is selected by writing the MODE bits to 100b in
The USART allows the user to control a bidirectional synchronous serial communications in master mode. The SCLK
pin is the output of the USART transmitter clock. No clock pulses are sent to the SCLK pin during start bit and stop bit.
The CPOL bit in
register allows the user to select the clock polarity, and the CPHA bit allows the user
to select the phase of the clock.
During the Idle state, preamble and send break, the external SCLK clock is not activated. In synchronous mode the
USART transmitter works exactly like in asynchronous mode. But as SCLK is synchronized with TX (according to
CPOL and CPHA), the data on TX is synchronous.
In synchronous mode, the USART receiver works in a different manner compared to the asynchronous mode. If
Receiver is enabled (RXEN=1), the data is sampled on SCLK (depending on CPOL and CPHA) without any
oversampling. A setup and a hold time must be respected (which depends on the baud rate: 1/16 bit time).
Note:
The SCLK pin works in conjunction with the UTXD pin, so the clock is provided only if TXEN=1
register, and a data is being transmitted (the data register USART_DR has
been written). This means that it is not possible to receive a synchronous data without
transmitting data.
The CPOL and CPHA bits in
register have to be selected when both
the transmitter and the receiver are disabled (TXEN=0 and RXEN=0) to ensure that the clock
pulses function correctly. These bits should not be changed while the transmitter or the
receiver is enabled (TXEN=1 and RXEN=1).
The Synchronous mode supports master mode only, it can NOT receive or send data related to
an input clock (SCLK is always an output).
Содержание SN32F755
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