UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
979 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
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.
37.7.6 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
ISO 7816 class A, B, or C power requirements, be aware of the logic level tolerances and
requirements when communicating or powering cards that use different power rails than
this part.
37.7.6.1 Smart card set-up procedure
A T = 0 protocol transfer consists of 8-bits of data, an even parity bit, and two guard bits
that allow for the receiver of the particular transfer to flag parity errors through the NACK
response (see
). Extra guard bits may be added according to card
requirements. If no NACK is sent (provided the interface accepts them in SCICTRL), the
next byte may be transmitted immediately after the last guard bit. If the NACK is sent, the
transmitter will retry sending the byte until successfully received or until the SCICTRL
retry limit has been met.
Fig 117. 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