
15-10
MCF5249UM
MOTOROLA
Operation
15.3.3.3
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-transmitter link is disabled. This mode is useful for testing remote channel receiver and
transmitter operation. While in this mode, the receiver clocks the transmitter.
Note: Because the receiver is not active, the CPU cannot read received data. All status
conditions are inactive. Received parity is not checked and is not recalculated for
transmission. Stop bits are transmitted as received. A received break is echoed as
received until the next valid start bit is detected.
Figure 15-7 Looping Modes Functional Diagram
15.3.4
MULTIDROP MODE
The UART can be programmed to operate in a wakeup mode for multidrop or multiprocessor applications.
Functional timing information for the multidrop mode is shown in
Figure 15-8. The mode is selected by
setting bits 3 and 4 in UART mode register 1 (UMR1). This mode of operation connects the master station
to several slave stations (maximum of 256). In this mode, the master transmits an address character
followed by a block of data characters targeted for one of the slave stations. The slave stations channel
receivers are disabled; however, they continuously monitor the data stream sent out by the master station.
When the master sends an address character, the slave receiver channel notifies its respective CPU by
setting the RxRDY bit in the USR and generating an interrupt (if programmed to do so). Each slave station
CPU then compares the received address to its station address and enables its receiver if it wants to
CPU
Rx
Tx
CPU
Rx
Tx
(a) Automatic Echo
(b) Local Loopback
(c) Remote Loopback
RxD
Input
RxD
Input
RxD
Input
TxD
Output
TxD
Output
TxD
Output
Disabled
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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