Motorola ColdFire MCF5281 - Manual (Page 444)

UART Modules
23-24 Freescale Semiconductor
Figure 23-23. Remote Loopback
23.4.4 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 receivers disabled, they continuously monitor the master’s data stream.
When the master sends an address character, the slave receiver 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. Unaddressed slave stations 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 23-24 .
CPU
Disabled
Disabled
Tx
Rx
Disabled
Disabled
UTXDn Output
URXDn Input
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3