Multiprocessor Communication Function - Renesas H8SX/1500 Series Hardware Manual

Section 12 Serial Communication Interface (SCI)
12.5

Multiprocessor Communication Function

Use of the multiprocessor communication function enables data transfer to be performed among a
number of processors sharing communication lines by means of asynchronous serial
communication using the multiprocessor format, in which a multiprocessor bit is added to the
transfer data. When multiprocessor communication is carried out, each receiving station is
addressed by a unique ID code. The serial communication cycle consists of two component cycles:
an ID transmission cycle which specifies 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. If the multiprocessor bit is 1, the cycle is an ID
transmission cycle, and if the multiprocessor bit is 0, the cycle is a data transmission cycle.
Figure 12.10 shows an example of inter-processor communication using the multiprocessor
format. The transmitting station first sends data which includes the ID code of the receiving
station and a multiprocessor bit set to 1. It then transmits transmit data added with the
multiprocessor bit cleared to 0. The receiving station skips data until data with the multiprocessor
bit set to 1 is sent. When data with the multiprocessor bit set to 1 is received, the receiving station
compares that data with its own ID. The station whose ID matches then receives the data sent next.
Stations whose ID does not match continue to skip data until data with the multiprocessor bit set
to 1 is again received.
The SCI uses the MPIE bit in SCR to implement this function. When the MPIE bit is set to 1,
transfer of receive data from RSR to RDR, error flag detection, and setting the SSR status flags,
RDRF, FER, and ORER in SSR to 1 are prohibited until data with the multiprocessor bit set to 1 is
received. On reception of a receive character with the multiprocessor bit set to 1, the MPBR bit in
SSR is set to 1 and the MPIE bit is automatically cleared, thus normal reception is resumed. If the
RIE bit in SCR is set to 1 at this time, an RXI interrupt is generated.
When the multiprocessor format is selected, the parity bit setting is invalid. All other bit settings
are the same as those in normal asynchronous mode. The clock used for multiprocessor
communication is the same as that in normal asynchronous mode.
Rev. 3.00 Mar. 14, 2006 Page 416 of 804
REJ09B0104-0300