Datasheet

UART Modules
12-12 MCF5206e USER’S MANUAL MOTOROLA
the receiver asserts RTS. Using this mode of operation prevents overrun errors by
connecting the RTS to the CTS input of the transmitting device.
To use the RTS signals on UART 2, you must set up the MCF5206e Pin Assignment
Register (PAR) in the SIM to enable the corresponding I/O pins for these functions. If the
FIFO stack contains characters and the receiver is disabled, the CPU can still read the
characters in the FIFO. If the receiver is reset, the FIFO stack and all receiver status bits,
corresponding output ports, and interrupt request are reset. No additional characters are
received until the receiver is re-enabled.
12.3.3 Looping Modes
You can configure the UART to operate in various looping modes as shown in Figure 12-
7. These modes are useful for local and remote system diagnostic functions. The modes
are described in the following paragraphs with additional information available in
subsection 12.4 Register Description and Programming.
You should only switch between modes while the transmitter and receiver are disabled
because the selected mode is activated immediately on mode selection, even if this
occurs in the middle of character transmission or reception. In addition, if a mode is
deselected, the device switches out of the mode immediately, except for automatic echo
and remote echo loopback modes. In these modes, the deselection occurs just after the
receiver has sampled the stop bit (this is also the one-half point). For automatic echo
mode, the transmitter stays in this mode until the entire stop bit has been retransmitted.
12.3.3.1 AUTOMATIC ECHO MODE. In this mode, the UART automatically retransmits
the received data on a bit-by-bit basis. The local CPU-to-receiver communication
continues normally but the CPU-to-transmitter link is disabled. While in this mode,
received data is clocked on the receiver clock and retransmitted on TxD. The receiver
must be enabled but not the transmitter. Instead, the transmitter is clocked by the receiver
clock.
Because the transmitter is not active, the TxEMP and TxRDY bits in USR are inactive and
data is transmitted as it is received. Received parity is checked but not recalculated for
transmission. Character framing is also checked but stop bits are transmitted as received.
A received break is echoed as received until the next valid start bit is detected.
12.3.3.2 LOCAL LOOPBACK MODE. In this mode, TxD is internally connected to RxD.
This mode is useful for testing the operation of a local UART module channel by sending
data to the transmitter and checking data assembled by the receiver. In this manner,
correct channel operations can be assured. Both transmitter and CPU-to-receiver
communications continue normally in this mode. While in this mode, the RxD input data
is ignored, the TxD is held marking, and the receiver is clocked by the transmitter clock.
The transmitter must be enabled but not the receiver.
12.3.3.3 REMOTE LOOPBACK MODE. In this mode, the channel automatically
transmits received data on the TxD output on a bit-by-bit basis. The local CPU-to-
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