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Remote I/O Communications Characteristics Section 6-1
Refresh Time The refresh time is the time required for I/O data to be exchanged between
the PC’s CPU and the DeviceNet Master Unit. The PC’s cycle time is
increased when a Master Unit is mounted, as shown below.
Note Refer to the PC’s Operation Manual for more details on the refresh time and
the PC’s cycle time.
Master Unit for CV-series PCs (CVM1-DRM21)
The PC’s cycle time is increased by 1.1 ms. This is the extra time required for
CPU Bus Unit servicing (DeviceNet Master Unit refreshing).
Master Unit for C200HX, C200HG, C200HE, and C200HS PCs (C200HW-
DRM21)
The PC’s cycle time is increased by the amount shown below. The extra time
is required for I/O refreshing.
The number of words refreshed is the total number of words in the I/O area
that are used by the Slaves, including any unused words between words actu-
ally used by the Slaves. For example, if there are only two Input Slaves with
node numbers 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.
6-1-3 I/O Unit Interface Cycle Time
The I/O Unit interface cycle time is the time interval between the I/O process-
ing of I/O Units in a MULTIPLE I/O TERMINAL and the next I/O processing for
those I/O Units.
Without a Special I/O Unit If there is not a Special I/O Unit, the I/O Unit interface cycle time can be calcu-
lated using the following formula:
T
CYCIF
= 1.5 × MOD [ms]
MOD: Number of I/O data frames
If the total numbers of input bits and output bits are both 128 or
less: MOD = 1
If the either the total number of input bits or the total number of out-
put bits is more than 128: MOD = 2
With a Special I/O Unit More frames are required with a Special I/O Unit. There will be one additional
special I/O data frame per Special I/O Unit and one additional frame for
checking the status of all the Special I/O Units. Therefore, the I/O Unit inter-
face cycle time with a Special I/O Unit can be calculated using the following
formula:
T
CYCIF
= 1.5 × (MOD + N + 1) [ms]
MOD: Number of I/O data frames
If there is no ordinary I/O Unit:MOD = 0
If the total numbers of input bits and output bits are both 128 or
less:MOD = 1
If the either the total number of input bits or the total number of out-
put bits is more than 128: MOD = 2
N: Number of Special I/O Units (1 to 8)
PC DeviceNet Unit I/O refreshing time (ms)
C200HX, C200HG,
and C200HE
1.72 + 0.022 × the number of words refreshed
C200HS 2.27 + 0.077 × the number of words refreshed
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