C8051F300_08 Datasheet, PDF (135/179 Pages) Silicon Laboratories – Mixed Signal ISP Flash MCU Family

C8051F300/1/2/3/4/5
14.3. Multiprocessor Communications
9-Bit UART mode supports multiprocessor communication between a master processor and one or more
slave processors by special use of the ninth data bit. When a master processor wants to transmit to one or
more slaves, it first sends an address byte to select the target(s). An address byte differs from a data byte
in that its ninth bit is logic 1; in a data byte, the ninth bit is always set to logic 0.
Setting the MCE0 bit (SCON.5) of a slave processor configures its UART such that when a stop bit is
received, the UART will generate an interrupt only if the ninth bit is logic one (RB80 = 1) signifying an
address byte has been received. In the UART interrupt handler, software will compare the received
address with the slave's own assigned 8-bit address. If the addresses match, the slave will clear its MCE0
bit to enable interrupts on the reception of the following data byte(s). Slaves that weren't addressed leave
their MCE0 bits set and do not generate interrupts on the reception of the following data bytes, thereby
ignoring the data. Once the entire message is received, the addressed slave resets its MCE0 bit to ignore
all transmissions until it receives the next address byte.
Multiple addresses can be assigned to a single slave and/or a single address can be assigned to multiple
slaves, thereby enabling "broadcast" transmissions to more than one slave simultaneously. The master
processor can be configured to receive all transmissions or a protocol can be implemented such that the
master/slave role is temporarily reversed to enable half-duplex transmission between the original master
and slave(s).
Master
Device
RX
TX
Slave
Device
RX
TX
Slave
Device
RX
TX
Slave
Device
+5V
RX
TX
Figure 14.6. UART Multi-Processor Mode Interconnect Diagram
Rev. 2.9
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