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101
2. APPLICAT ION
MITSUBISHI MICROCOMPUTER
3819 Group
2.3 Serial I/O
3819 Group USER’S MANUAL
(3) Cyclic transmission or reception of block data (data of a specified number of bytes) between microcomputers
[without using an automatic transfer]
Outline :
When a clock synchronous serial I/O is used for communication, synchronization of the clock and the
data between the transmitter and receiver sides may be lost because of noise included in the
synchronizing clock. Thus, it is necessary to be corrected constantly. This “heading adjustment” is carried
out by using the interval between blocks in this example.
Fig. 2.3.23 Connection diagram [Cyclic transmission or reception of block data between microcomputers]
Specifications :
Synchronous clock frequency : 131 kHz (f(X
IN
) = 4.19 MHz is divided by 32)
Byte cycle : 488
μ
s
Number of bytes for transmission or reception : each 8 byte/block
Block transmission cycle : 16 ms
Block transmission period : 3.5 ms
Interval between blocks : 12.5 ms
Heading adjustive time : 8 ms
Transmission direction : LSB first
Limitations of the specifications
1. Reading of the reception data and setting of the next transmission data must be completed within the time
obtained from “byte cycle – time for transmitting 1-byte data” (in this example, the time taken from generating
of the Serial I/O 1 interrupt request to generating of the next synchronizing clock is 431
μ
s).
2. “Heading adjustive time < interval between blocks” must be satisfied.
3. Although the transmission direction can be switched for the Serial I/O of 3819 group, it cannot be
switched for some serial I/Os of 740 family including 38000 series (only LSB first). Be sure to check when
deciding specifications.
S
CLK
S
IN
S
OUT
Master unit
S
CLK
S
IN
S
OUT
Slave unit