451
Remote I/O Communications Characteristics Section 8-1
Input Slaves, Output
Slaves, or Mixed I/O
Slaves with More than 8
Bytes of I/O
T
RT
= T
OH
+ T
BYTE-IN
× B
IN
+ T
BYTE-OUT
× B
OUT
[ms]
T
-OH
: The overhead protocol
T
BYTE-IN
: The input byte transmission time
B
IN
: The number of input bytes
T
BYTE-OUT
: The output byte transmission time
B
OUT
: The number of output bytes
The number of output bytes (B
OUT
) for Input Slaves only is 0, and the number
of input bytes (B
IN
) for Output Slaves only is 0.
Refresh Time The refresh time is the time required for I/O data to be exchanged between
the PLC's CPU Unit and the DeviceNet Master Unit. The PLC's cycle time is
increased when a Master Unit is mounted, as shown below.
Note Refer to the PLC's Operation Manual for more details on the refresh time and
the PLC's cycle time.
Master Unit for CV-series
PLCs
The PLC's cycle time (CPU Bus Unit servicing) is increased by the amount
shown in the following table when a Master Unit is mounted to the PLC.
Master Unit for CS, CJ,
C200HX/HG/HE (-Z), and
C200HS PLCs
The PLC's cycle time (I/O refreshing) is increased by the amount shown in the
following table when a Master Unit is mounted to the PLC.
Note The number of words refreshed is the total number of words in the I/O Area
that are allocated to the Slaves, including any unused words between those
words actually used by the Slaves.
For example, if there are only two Input Slaves with node addresses 1 and 5,
the 5 input words for nodes 1 through 5 would be refreshed even though the
input words for nodes 2, 3, and 4 are unused.
If message communications are being performed, just add the number of
words used in message communications to the above number of words for
whenever messages are being processed.
8-1-3 More than One Master in Network
The following equation shows the communications cycle time (T
RM
) when
there is more than one Master in the Network.
An example for two Master Units is shown here.
Baud rate T
OH
T
BYTE-IN
T
BYTE-OUT
500 kbps 0.306 ms 0.040 ms 0.036 ms
250 kbps 0.542 ms 0.073 ms 0.069 ms
125 kbps 1.014 ms 0.139 ms 0.135 ms
Process Processing time
CPU Bus Unit servicing DeviceNet Unit refreshing: 1.1 ms
Process Processing time
I/O refreshing DeviceNet Unit I/O refreshing:
Using Master Unit for CS, CJ, and C200HX/HG/HE (-Z)
PLCs
1.72 + 0.022 × number of words (ms) (See note.)
Using Master Unit for C200HS PLCs
2.27 + 0.077 × number of words (ms) (See note.)
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