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Remote I/O Communications Characteristics Section 8-1
Slaves with More Than 8
Bytes of Input or Out put
T
RT
= T
OH
+ T
BYTE-IN
× B
IN
+ T
BYTE-OUT
× B
OUT
[ms]
T
OH
: Protocol overhead
T
BYTE-IN
: The input byte transmission time
B
IN
: The number of input words
T
BYTE-OUT :
The output byte transmission time
B
OUT :
The number of output words
For Input Slaves take B
OUT
to be 0, and for Output Slaves take B
IN
to be 0.
Refresh Time
The refresh time is the time required for I/O data to be exchanged between
the PC’s CPU Unit and the DeviceNet Unit. The CPU Unit’s cycle time is
increased when a DeviceNet Unit is mounted, as shown below.
Note 1. 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
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.
2. 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.
3. When the message communications are performed, an event execution
time must be added to the PC cycle time.
4. For details about refresh time or PC cycle time, refer to operation manual
of the PC.
8-1-2 I/O Response Time
Maximum I/O Response Time
Communications Cycle
Time ≥ PC Cycle Time
The maximum I/O response time will be as shown below if the DeviceNet Unit
takes in data immediately after I/O refreshing and if the communications cycle
time is longer than the PC cycle time.
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
Processing item Processing time
I/O refresh DeviceNet Unit I/O refreshing time (ms)
0.7 + 0.001 × the number of words refreshed (See note 1.)
ON input data
notice delayed
Communications cycle
Instruction
execution
Instruction
execution
Instruction
execution
PC
Transfers to the
shared RAM
when PC scan is
completed.
Takes into the
PC's internal
memory.
Slave