Message Communication Characteristics - Omron GRT1 - 27-11-2006 Operation Manual

Remote Communication Characteristics
Note
3-5-2

Message Communication Characteristics

Communication Time to
the PROFIBUS
Communication Unit
Communication Time to
the SmartSlice I/O Unit
Note
58
1. The processing time required for an input signal on an input terminal to be
transferred to a PROFIBUS input data message is of the same order of
magnitude as the numbers presented above.
2. Setting the DIP switches to OFF, will extend the processing time with an
approximate 2 ms.
The message communication time is the time required for a message sent to
the SmartSlice I/O System to travel over the Network and arrive at the Smart-
Slice I/O Unit. (The message may be data from a SEND(090)/RECV(098)
instruction or a FINS command from a CMND(490)/IOWR(223) instruction.)
The time required for a message to be sent is the same as the PROFIBUS
cycle time, since the acyclic message are sent at the end of a cycle, prior to
the next one.
If a SmartSlice I/O Unit is the final message destination, the message com-
munication time over the SmartSlice bus must be added to calculate the total
message communication time. Use the following equation to calculate the
message communication time over the Slice bus.
Message communication time = T
Number of frames = Number of message bytes ÷ 30 (round up fractions)
1. If the CPU Unit attempts to send another message or receives a message
from another station before the message communication time has finished,
the response message being sent or the message being received from an-
other station may be destroyed. Always perform message communication
at intervals longer than the message communication time and use mes-
sage instructions (SEND(090), RECV(098), CMND(490), and IO-
WR(223)). Never send messages to any one station at intervals less than
the message communication time.
If send or receive messages are destroyed, the error record will be placed
in the error history of the Master Unit. If an error occurs, read the error his-
tory using the FINS command or monitor the error history from the Config-
urator.
2. The above equations provide find the approximate message communica-
tion time, but not the maximum time. The message communication time
will depend on the frequency of the message communication, the load on
the remote station, the communication cycle time, and other factors. For
any one Master Unit, the message communication time may be greatly in-
creased due to heavy loads.
× Number of frames
SL
Section 3-5