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Remote I/O Communications Characteristics Section 8-1
Communications Cycle
Time Calculation
Use the equations shown below to calculate the communications cycle time
(T
RM
) for a network with one Master. Note that if the result of this calculation is
less than 2 ms, the actual communications cycle time will be 2 ms.
T
RM
= Σ (Communications time per Slave)
+ High-density Unit processing time
+ Explicit message processing time
+ COS/Cyclic connection time (ms)
+ 0.01 × N + 1.0 [ms]
Communications Time per Slave:
This is the communications time required for a single Slave.
“Σ (Communications time per Slave)” represents the total of the “Communica-
tions time per Slave” for all the Slaves in the network.
High-density Unit Processing Time:
3.5 ms
This is added if there are any Slaves in the network that use at least 8 bytes
for input, output, or both.
Explicit Message Processing Time:
(0.11 × T
B
) × n [ms]
Only added when explicit communications (sending or receiving) are per-
formed.
n= Number of explicit messages (both sending and receiving) that occur in
one cycle time
T
B
= The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
COS/Cyclic Connection Time:
{(0.05+0.008 × S) × T
B
} × n (ms)
S: Total number of inputs and outputs in the COS/cycle connection (bytes)
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
n: Number of nodes occurring simultaneously within 1 communications cycle
time in the COS/Cyclic connection
N: Number of Slaves
Communications Time/Slave
The communications time per Slave is the communications time required for a
single Slave.
The following equations show the communications time/Slave (T
RT
) for each
kind of Slave Unit.
Output Slaves with Less
Than 8 Bytes of Output
T
RT
= 0.016 ×T
B
× S
OUT1
+ 0.11 × T
B
+ 0.07 [ms]
S
OUT1
: The number of Output Slave output words
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
Input Slaves with Less
Than 8 Bytes of Input
T
RT
= 0.016 ×T
B
× S
IN1
+ 0.06 × T
B
+ 0.05 [ms]
S
IN1
: The number of Input Slave input words
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
Mixed I/O Slaves with Less
Than 8 Bytes of Input or
Output
T
RT
= 0.016 × T
B
× (S
OUT2
+ S
IN2
) + 0.11 × T
B
+ 0.07 [ms]
S
OUT2
: The number of Mixed I/O Slave output words
S
IN2
: The number of Mixed I/O Slave input words
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)