
R8C/3GM Group
22. Serial Interface (UART2)
R01UH0284EJ0100 Rev.1.00
Aug 09, 2011
22.6
Multiprocessor Communication Function
When the multiprocessor communication function is used, data transmission/reception can be performed between a
number of processors sharing communication lines by asynchronous serial communication, in which a
multiprocessor bit is added to the data. For multiprocessor communication, each receiving station is addressed by a
unique ID code. The serial communication cycle consists of two component cycles; an ID transmission cycle for
specifying the receiving station, and a data transmission cycle for the specified receiving station. The
multiprocessor bit is used to differentiate between the ID transmission cycle and the data transmission cycle. When
the multiprocessor bit is set to 1, the cycle is an ID transmission cycle; when the multiprocessor bit is set to 0, the
The transmitting station first sends the ID code of the receiving station to perform communication as
communication data with a 1 multiprocessor bit added. It then sends transmit data as communication data with a 0
multiprocessor bit added.
When communication data in which the multiprocessor bit is 1 is received, the receiving station compares that data
with its own ID. If they match, the data to be sent next is received. If they do not match, the receive station
continues to skip communication data until data in which the multiprocessor bit is 1 is again received.
UART2 uses the MPIE bit in the U2SMR5 register to implement this function. When the MPIE bit is set to 1, data
transfer from the UART2 receive register to the U2RB register, receive error detection, and the settings of the
status flags, the RI bit in the U2C1 register, bits FER and OER in the U2RB register, are disabled until data in
which the multiprocessor bit is 1 is received. On receiving a receive character in which the multiprocessor bit is 1,
the MPRB bit in the U2RB register is set to 1 and the MPIE in the U2SMR5 register bit is set to 0, thus normal
reception is resumed.
When the multiprocessor format is specified, the parity bit specification is invalid. All other bit settings are the
same as those in normal asynchronous mode (UART mode). The clock used for multiprocessor communication is
the same as that in normal asynchronous mode (UART mode).
Figure 22.17
Inter-Processor Communication Example Using Multiprocessor Format
(Data AAh Transmission to Receiving Station A)
01h
Serial data
AAh
(MPRB = 1)
(MPRB = 0)
ID transmission cycle
= receiving station
specification
Data transmission cycle
= data transmission to
receiving station
specified by ID
MPRB: Multiprocessor bit
(ID = 01)
(ID = 02)
(ID = 03)
(ID = 04)
Receiving
station A
Receiving
station B
Receiving
station C
Receiving
station D
Transmitting
station
Communication line