Message Communications Characteristics - Omron SMARTSLICE - 04-2008 Operation Manual

Message Communications Characteristics

Slice Bus
Communications
Time
(T and T
SL-IN SL-OUT
5-2 Message Communications Characteristics
5-2-1 Message Communications Time
Communications
Time to the DeviceNet
Communications Unit
Communications
Time to the Slice I/O
Unit
Note
66
The Slice bus communications time is the time required to communicate with
an Input Unit (T
SL-IN
T = 0.01 × number of input data bytes [ms]
SL-IN
)
T = 0.18 + total number of output data bytes × 0.002 [ms]
SL-OUT
The message communications time is the time required for a message sent to
the Slice I/O Terminal to travel over the Network and arrive at the Slice I/O
Terminal. (The message may be data from a SEND(090)/RECV(098) instruc-
tion or a FINS command from a CMND(490)/IOWR(223) instruction.)
Use the following equation to calculate the message communications time to
the DeviceNet Communications Unit.
Message communications time = DeviceNet communications cycle time
(T ) × {(Number of message bytes + 15) ÷ 6 + 1}
RM
The number of message bytes is the number of bytes of data after the FINS
command's command code. The equation for the DeviceNet communications
cycle time (T
RM
If a Slice I/O Unit is the final message destination, the message communica-
tions time over the Slice bus must be added to calculate the total message
communications time. Use the following equation to calculate the message
communications time over the Slice bus.
Message communications 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 node before the message communications time has fin-
ished, the response message being sent or the message being received
from another node may be destroyed. Always perform message commu-
nications at intervals longer than the message communications time and
use message instructions (SEND(090), RECV(098), CMND(490), and
IOWR(223)). Never send messages to any one node at intervals less
than the message communications 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
history using the FINS command or monitor the error history from the
Configurator.
(2) The above equations provide find the approximate message communica-
tions time, but not the maximum time. The message communications
time will depend on the frequency of the message communications, the
load on the remote node, the communications cycle time, and other fac-
tors. For any one Master Unit, the message communications time may be
greatly increased due to heavy loads.
) or Output Unit (T
SL-OUT
) is in 5-1 Remote I/O Communications Characteristics.
SL
Section 5-2
) in the Slice I/O Terminal.
× Number of frames