Motorola MCF5282, MCF5281 user manual Multidrop Mode, Remote Loop-Back Mode

Models: MCF5282 MCF5281

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Operation

UTXDn is held marking

The receiver is clocked by the transmitter clock. The transmitter must be enabled, but the receiver need not be.

23.5.3.3Remote Loop-Back Mode

In remote loop-back mode, shown in Figure 23-24,the channel automatically transmits received data bit by bit on the UTXDn output. The local CPU-to-transmitter link is disabled. This mode is useful in testing receiver and transmitter operation of a remote channel. For this mode, the transmitter uses the receiver clock.

Because the receiver is not active, received data cannot be read by the CPU and all status conditions are inactive. Received parity is not checked and is not recalculated for transmission. Stop bits are sent as they are received. A received break is echoed as received until the next valid start bit is detected.

CPU

Disabled

 

Rx

 

Disabled

 

 

 

 

URXDn Input

Disabled

 

Disabled

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tx

 

 

 

 

UTXDn Input

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 23-24. Remote Loop-Back

23.5.4 Multidrop Mode

Setting UMR1n[PM] programs the UART to operate in a wake-up mode for multidrop or multiprocessor applications. In this mode, a master can transmit an address character followed by a block of data characters targeted for one of up to 256 slave stations.

Although slave stations have their channel receivers disabled, they continuously monitor the master’s data stream. When the master sends an address character, the slave receiver channel notifies its respective CPU by setting USRn[RxRDY] 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 wishes to receive the subsequent data characters or block of data from the master station. Slave stations not addressed continue monitoring the data stream. Data fields in the data stream are separated by an address character. After a slave receives a block of data, its CPU disables the receiver and repeats the process. Functional timing information for multidrop mode is shown in Figure 23-25.

23-26

MCF5282 User’s Manual

MOTOROLA

Page 500
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Motorola MCF5282, MCF5281 user manual Multidrop Mode, Remote Loop-Back Mode