Silicon Laboratories C8051F347 - Manual (Page 217)

Rev. 1.3 217
C8051F340/1/2/3/4/5/6/7/8/9/A/B/C/D
space is made available in the FIFO for another incoming byte. If enabled, an interrupt will occur when RI1
is set. RI1 can only be cleared to '0' by software when there is no more information in the FIFO. The rec-
ommended procedure to empty the FIFO contents is as follows:
1. Clear RI1 to '0'.
2. Read SBUF1.
3. Check RI1, and repeat at step 1 if RI1 is set to '1'.

If the extra bit function is enabled (XBE1 = ‘1’) and the parity function is disabled (PE1 = ‘0’), the extra bit
for the oldest byte in the FIFO can be read from the RBX1 bit (SCON1.2). If the extra bit function is not
enabled, the value of the stop bit for the oldest FIFO byte will be presented in RBX1. When the parity func-
tion is enabled (PE1 = ‘1’), hardware will check the received parity bit against the selected parity type
(selected with S1PT[1:0]) when receiving data. If a byte with parity error is received, the PERR1 flag will be
set to ‘1’. This flag must be cleared by software. Note: when parity is enabled, the extra bit function is not
available.
19.3.3. Multiprocessor Communications
UART1 supports multiprocessor communication between a master processor and one or more slave pro-
cessors by special use of the extra 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 extra bit is logic 1; in a data byte, the extra bit is always set to logic 0.
Setting the MCE1 bit (SMOD1.7) of a slave processor configures its UART such that when a stop bit is
received, the UART will generate an interrupt only if the extra bit is logic 1 (RBX1 = 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 address. If the addresses match, the slave will clear its MCE1 bit to
enable interrupts on the reception of the following data byte(s). Slaves that weren't addressed leave their
MCE1 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 MCE1 bit to ignore all trans-
missions 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 Slave
Device
TX RX RX TX
Slave
Device
RX TX
Slave
Device
RX TX
V+