24: R
EMOTE
I/O S
YSTEM
24-12
O
PEN
N
ET
C
ONTROLLER
U
SER
’
S
M
ANUAL
Calculation of the INTERBUS Cycle Time
The I/O data is refreshed continuously. The cycle time of the INTERBUS system
depends on few factors and increases almost linearly with an increasing number
of I/O points. Due to the high effectiveness of the protocol, the greater part of the
cycle time is determined by the number of I/O points. However, it is also required
to consider quantities such as the number of installed remote bus devices, the
duration of the check sequence, the firmware runtime, and the signal runtime on
the transmission medium.
Remote I/O slave stations have a specific data length depending on the I/O type. The data length (register width) is a factor
to determine the cycle time.
The cycle time (refresh time) can be calculated according to:
t
cycle
= {K
×
13
×
(6 + n) + 4
×
m}
×
t
Bit
+ t
SW
+ t
PH
+ r
×
t
W
whereby
t
cycle
INTERBUS cycle time (1 scan time)
K
1.15
n
Number of user data bytes
m
Number of installed remote bus devices
t
Bit
Bit duration (0.002 msec)
t
SW
Firmware run time (1 msec)
t
PH
Signal run time on the transmission medium (0.016 msec/km)
r
1
t
W
13
×
2 µsec conversion time
Note:
Data exchange between the OpenNet Controller CPU module and the remote I/O master module is asynchronous with
the INTERBUS cycle time.
Start and Stop of Remote I/O Communication
The remote I/O master module is powered by the CPU module. The remote I/O communication is started and stopped by
turning power on and off to the CPU module.
After connecting remote I/O slave modules to the remote I/O master module using INTERBUS cable, power up the slave
modules first, followed by the CPU module at the remote I/O master station.
The start delay after power-up depends on the contents of the user program, remote I/O system setup, and data link config-
uration. A rough estimate of the start delay is the operation start time depending on the user program size plus approxi-
mately 4 seconds.
While the CPU module is powered up and program operation is stopped, the remote I/O network is in the run state but the
data exchange between the CPU and the remote I/O master module is stopped.
SX5S Type No.
Slave Module Name
Inputs
Outputs
Register Width
(user data bytes n)
SX5S-SBN16S/-SBN16K
16-input module
2 bytes
—
2 bytes
SX5S-SBR08
8-relay output module
—
2 bytes
2 bytes
SX5S-SBT16K/-SBT16P
16-output module
—
2 bytes
2 bytes
SX5S-SBM16K/-SBM16P
Mixed I/O module
1 byte
1 byte
1 byte
Cycle Time Examples
I/O Points
Cycle Time
512
2.1 msec
1024
4.0 msec
2048
7.5 msec
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