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6. PRECAUTIONS WHEN DESIGNING A SCREEN
MELSEC-A
6.9
Method for Speeding Up the Monitoring Display
To speed up the monitoring display;
Decrease monitoring number of points set per screen and reduce the
number of access times to the PC CPU. (Decrease the number of
monitoring data collection times)
• Make the monitoring figure small, and shorten the graphic display time.
To improve the monitoring display speed, design a monitor screen and a
sequence program with the following in mind.
6.9.1
Reduce the number of access times to the PC CPU
Data collection time of a monitored device can be shortened by decreasing
the number of monitored devices that are registered in one screen.
(When a PC CPU is executing END, FEND, or COM instruction, the G-con-
troller can communicate with a PC CPU one time. The number of the devices
that can be used for read/write of a device by communicating one time varies
according to the function registered for monitoring.)
(1)
128 bytes of data can be read during communications with a PC CPU at
one time by setting the monitored device at "CONTINUOUS".
When a monitored device is set at "RANDOM", 40 bytes of data are read
by communicating with the PC CPU one time.
In addition, the amount of canvas data (monitoring data stored in a
ROM/memory card) can be reduced by setting "CONTINUOUS".
The graph display function, block data display function can be set for
"CONTI NUOUS".
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(2)
By setting the data collection trigger condition to "leading/falling edge",
the number of times data read operations are done can be reduced.
Only when the data collection condition is satisfied, is the monitoring
function for which data coilection trigger condition is set to "leading/faIl-
ing edge" enabled to read and display monitor devices.
Max. 40 points data collection trigger condition devices are usually read
per one time.
Then, examination takes place to see whether data
collection condition was satisfied. Data collection trigger condition of 40
points of monitoring function can be checked during one-time com-
munications with a PC CPU. Therefore, the number of times of data read
can be reduced.
If data collection condition is set at "NORMALLY", all monitoring devices
are normally read. Therefore, the number of communication times with
a PC CPU increases.
6-41
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