Information
Enable single-wire operation by setting the C1[LOOPS] bit and the receiver source bit,
C1[RSRC]. Setting the C1[LOOPS] bit disables the path from the unsynchronized
receiver input signal to the receiver. Setting the C1[RSRC] bit connects the receiver input
to the output of the TXD pin driver. Both the transmitter and receiver must be enabled
(C2[TE] = 1 and C2[RE] = 1). When C7816[ISO_7816EN] is set, it is not a requirement
that both C2[TE] and C2[RE] are set.
45.4.6 Loop operation
In loop operation the transmitter output goes to the receiver input. The unsynchronized
receiver input signal is disconnected from the UART.
RXD
Tx pin output
RXINV
TXINV
TRANSMITTER
RECEIVER
Figure 45-242. Loop operation (C1[LOOPS] = 1, C1[RSRC] = 0)
Enable loop operation by setting the C1[LOOPS] bit and clearing the C1[RSRC] bit.
Setting the C1[LOOPS] bit disables the path from the unsynchronized receiver input
signal to the receiver. Clearing the C1[RSRC] bit connects the transmitter output to the
receiver input. Both the transmitter and receiver must be enabled (C2[TE] = 1 and
C2[RE] = 1). When C7816[ISO_7816EN] is set, it is not a requirement that both C2[TE]
and C2[RE] are set.
45.4.7 ISO-7816 / smartcard support
The UART provides mechanisms to support the ISO-7816 protocol that is commonly
used to interface with smartcards. The ISO-7816 protocol is an NRZ, single wire, half-
duplex interface. The TxD pin is used in open-drain mode since the data signal is used for
both transmitting and receiving. There are multiple subprotocols within the ISO-7816
standard. The UART supports both T = 0 and T = 1 protocols. The module also provides
for automated initial character detection and configuration which allows for support of
both direct convention and inverse convention data formats. A variety of interrupts
specific to 7816 are provided in addition to the general interrupts to assist software.
Chapter 45 Universal Asynchronous Receiver/Transmitter (UART)
K10 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc. 1323