Multiprocessor Communication Function - Hitachi H8S/2338 Series Hardware Manual

11.3.3

Multiprocessor Communication Function

The multiprocessor communication function performs serial communication using the
multiprocessor format, in which a multiprocessor bit is added to the transfer data, in asynchronous
mode. Use of this function enables data transfer to be performed among a number of processors
sharing a single serial communication line.
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. The multiprocessor bit is used
to differentiate between the ID transmission cycle and the data transmission cycle.
The transmitting station first sends the ID of the receiving station with which it wants to perform
serial communication as data with a 1 multiprocessor bit added. It then sends transmit data as data
with a 0 multiprocessor bit added.
The receiving station skips the data until data with a 1 multiprocessor bit is sent.
When data with a 1 multiprocessor bit 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 the data until data with a 1 multiprocessor bit is again received. In this
way, data communication is carried out among a number of processors.
Figure 11-9 shows an example of inter-processor communication using the multiprocessor format.
Data Transfer Formats: There are four data transfer formats.
When the multiprocessor format is specified, the parity bit specification is invalid.
For details, see table 11-10.
Clock: See the section on asynchronous mode.
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