
2.CYCLIC TRANSMISSION DESCRIPTION B-63434EN/02
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Measures to guarantee the concurrency of multiple-byte data
An example of handling input data of multiple-byte on the second
ladder level to guarantee its concurrency is given below. To
establish the concurrency of data tens to hundreds of bytes long, it is
simple to perform data transmission with transmission of a message
with confirmation. For details of transmission of a message with
confirmation, see Section 3.7, "Server Function of Transmitting a
Message with Confirmation."
Example of measures: Control using a flag for synchronization
This control method provides a flag for synchronization before and
after multiple-byte data to synchronize the data. An example of
guaranteeing the concurrency of 6-byte data is described below.
1) Data structure
A flag for synchronization is provided in the byte preceding the
2-byte data and in the byte following the 2-byte data, thus
extending the 2-byte data to 8-byte data.
R0099 Flag 1 for
synchronization
R0100 Data section
R0105
R0106 Flag 2 for
synchronization
2) Processing by the data writing side
The data is updated according to the procedure below.
(1) Flag 1 for synchronization is incremented.
(2) The data section is updated.
(3) The same value as flag 1 for synchronization is set in flag 2
for synchronization.
3) Processing by the data reading side
The data is processed according to the procedure below.
(1) The eight bytes starting with R0099 are copied to the area
for synchronization (R0199) at the start of the second level.
(2) A check is made to see if R0199 = R0206.
(3) If R0199 = R0202, R0200 is processed as 6-byte data.
CAUTION
If the size of data to be synchronized is increased by
combining many bytes of data at a time, the data
may not be synchronized easily.
In such a case, divide the data at each variable, for
example, and provides flags for synchronization.