38K2 datasheet(205/358 Pages) RENESAS

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2.4 Serial I/O

Rev.2.00

Oct 15, 2006

page 56 of 112

38K2 Group

REJ09B0338-0200

APPLICATION

(3)

Cyclic transmission or reception of block data (data of specified number of bytes) between

two microcomputers

Outline : When the clock synchronous serial I/O is used for communication, synchronization of the

clock and the data between the transmitting and receiving sides may be lost because of

noise included in the synchronous clock. It is necessary to correct that constantly, using

“heading adjustment”.

This “heading adjustment” is carried out by using the interval between blocks in this

example.

Figure 2.4.24 shows a connection diagram.

Fig. 2.4.24 Connection diagram

Specifications :

• The serial I/O is used (clock synchronous serial I/O is selected).

• Synchronous clock frequency : 125 kHz (f(XIN) = 6 MHz is divided by 48)

• Byte cycle: 488

µs

• Number of bytes for transmission or reception : 8 byte/block

• Block transfer cycle : 16 ms

• Block transfer term : 3.5 ms

• Interval between blocks : 12.5 ms

• Heading adjustment time : 8 ms

Limitations of specifications :

• Reading of the reception data and setting of the next transmission data must be

completed within the time obtained from “byte cycle – time for transferring 1-byte

data” (in this example, the time taken from generating of the serial I/O receive

interrupt request to input of the next synchronous clock is 431

µs).

•“Heading adjustment time < interval between blocks” must be satisfied.

SCLK

Master unit

SCLK

Slave

TXD

RXD

TXD

RXD

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