(4) Multiprocessor Communication
The multiprocessor communication function enables several processors to share a single serial
communication line. The processors communicate in asynchronous mode using a format with an
additional multiprocessor bit (multiprocessor format).
In multiprocessor communication, each receiving processor is addressed by an ID.
A serial communication cycle consists of two cycles: an ID-sending cycle that identifies the
receiving processor, and a data-sending cycle. The multiprocessor bit distinguishes ID-sending
cycles from data-sending cycles.
The transmitting processor starts by sending the ID of the receiving processor with which it wants
to communicate as data with the multiprocessor bit set to “1.” Next the transmitting processor
sends transmit data with the multiprocessor bit cleared to “0.”
Receiving processors skip incoming data until they receive data with the multiprocessor bit set to
“1.”
After receiving data with the multiprocessor bit set to “1,” the receiving processor with an ID
matching the received data continues to receive further incoming data. Multiple processors can
send and receive data in this way.
Four formats are available. Parity-bit settings are ignored when a multiprocessor format is selected.
For details see table 8-7.
Figure 8-9. Example of Communication among Processors Using Multiprocessor Format
(Sending Data H'AA to Receiving Processor A)
Transmitting
processor
Receiving
processor A
Serial communication line
Receiving
processor B
Receiving
processor C
Receiving
processor D
(ID = 01)
(ID = 02)
(ID = 03)
(ID = 04)
Serial data
H'01
H'AA
(MPB = 1)
(MPB = 0)
ID-sending cycle:
receiving processor address
Data-sending cycle:
data sent to receiving
processor specified by ID
MPB: multiprocessor bit
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