H8SLASH3021 datasheet(395/712 Pages) RENESAS

395 / 712 page

11. Serial Communication Interface

Rev.2.00 Mar. 22, 2007 Page 371 of 684

REJ09B0352-0200

Figure 11.8 shows an example of SCI receive operation in asynchronous mode.

Start

bit

0/1

Stop

bit

Data

Parity

bit

Start

bit

0/1

Stop

bit

Data

Parity

bit

Idle (mark)

state

RDRF

FER

RXI

request

1 frame

Framing error,

ERI request

RXI interrupt handler

reads data in RDR and

clears RDRF flag to 0

Figure 11.8 Example of SCI Receive Operation (8-Bit Data with Parity and One Stop Bit)

11.3.3

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 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. When they receive data with the multiprocessor bit set to 1, receiving processors compare the

data with their IDs. The receiving processor with a matching ID continues to receive further

incoming data. Processors with IDs not matching the received data skip further incoming data

until they again receive data with the multiprocessor bit set to 1. Multiple processors can send and

receive data in this way.

Figure 11.9 shows an example of communication among different processors using a

multiprocessor format.

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