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UART Modules Disabled Rx Disabled URXDn Input Disabled UTXDn Output CPU Disabled Tx 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. MCF52223 ColdFire® Integrated Microcontroller Reference Manual, Rev. 4 23-24 Freescale Semiconductor
