Yaskawa 260IF DeviceNet System - Manual (Page 42)

4.2 Calculating Communications Cycle Times
4-9
4
4.2.3 Precautions on Setting the Communications Cycle Time
Set a communications cycle time that allows sufficient time for a response to be returned
from all Slaves. If the communications cycle time is set shorter than the I/O command trans-
mission time, the 260IF Module will ignore the communications cycle time until I/O com-
mands have been transmitted to all Slaves. In such cases, the set value will exceed the
display for maximum value on the CP-717 communications cycle time. Adjust the setting so
that the displayed maximum value does not exceed the set value.
1 If the maximum value on the communications cycle time exceeds the set value, the data in the Slaves
will not be refreshed within the cycle time. Adjust the setting after calculating the communications
cycle time to avoid delays in data refreshing.
2 The default setting for the communications cycle time is 0. If this setting is not changed, data will not
be refreshed within the cycle time, as explained above. Always change the setting to avoid this prob-
lem.
The 260IF Module has, in addition to the I/O communications function, a message commu-
nications function.
When using message communications, the communications cycle time must be increased
according to the volume of message communications data.
To calculate the appropriate communications cycle time, replace the number of output bytes
(No) and the number of input bytes (Ni) in the eight equations for calculating the communi-
cations times with Slaves (4.2.2 Calculating Communications Cycle Times) with the mes-
sage communications requirements and response data volume.
If there are multiple DeviceNet Masters in the communications network, find the sum of the
times required by each Master for communications with the Slaves, and use this to set the
communications cycle time.
Fig 4.3 Communications Cycle Times Settings for Multiple Masters
• Communications cycle time for Master 1
= ( Σ×(time with Slave of Master 1 ) + (Σ(time with Slave of Master 2)
• Communications cycle time for Master 2
= ( Σ×(time with Slave of Master 1 ) + (Σ(time with Slave of Master 2)
INFO
Master 1 Master 2
Slave Slave Slave Slave