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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
1150 of 1441
NXP Semiconductors
UM10503
Chapter 40: LPC43xx/LPC43Sxx USART0_2_3
Transmission of data during synchronous slave mode is most time-critical. First the
external serial input clock must be detected using edge detection logic. Then, data needs
to be shifted out and be stable before the sampling edge of the external serial clock.
Remark:
In this mode the u_clk period is allowed to be 4x the serial clock period.
40.7.5.3 Synchronous master mode
Synchronous master mode is enabled by setting the CSRC register bit to ‘1’. In this mode,
the external clock is generated internally by the baud-rate generation logic and is used to
clock the input and output serial data. The functionality of the baud-rate generation is
described in
. Auto-baud is not supported during synchronous mode. The
1x baud rate clock is used to shift out the serial output data and to sample the serial input
data.
Synchronous master mode behaves similar to the slave mode, except that the serial input
data is not registered at the interface but is clocked in the USART clock domain at the
sampling edge of the serial clock.
During synchronous master mode, when start and stop bits are transmitted, the user can
enable the external clock continuously using cscen bit of the Synchronous Mode Control
register. This allows the connected slave to transmit data even when no data is
transmitted by the master itself.
40.7.6 Smart card mode
shows a typical asynchronous smart card application.
When the SCIEN bit in the SCICTRL register (
) is set as described above, the
USART provides bidirectional serial data on the open-drain TXD pin. No RXD pin is used
when SCIEN is 1. The USART UCLK pin will output synchronously with the data at the
data bit rate. Software must use timers to implement character and block waiting times (no
hardware support via trigger signals is provided on this part). GPIO pins can be used to
control the smart card reset and power pins. Any power supplied to the card must be
externally switched as card power supply requirements often exceed source currents
possible on this part. As the specific application may accommodate any of the available
Fig 130. Typical smart card application
LPCxxxx
ISO 7816
Smart Card
pull-up
resistor
selectable
power rail
VCC
CLK
I/O
RST
Insertion Switch
Optional
Logic Level
Translation
pull-up
resistor
pull-up
resistor
GPIO
GPIO
GPIO
TXD
UCLK