Configuring Isochronous Mode - Siemens SIMATIC S7-1500 Function Manual

Configuring isochronous mode

You can operate I/O modules isochronously both as central I/O in SIMATIC S7-1500 and as
distributed I/O in a distributed I/O system.
You can also jointly operate central and distributed I/O on PROFINET IO isochronously.
The following sections describe the procedure for configuring this using examples.
Configuring at a glance
Setting parameters for isochronous operation of the I/O module
You use the properties of the I/O addresses of the corresponding I/O module to:
● Set isochronous mode for the module
● Assign the inputs and outputs of the module to a process image partition and an
isochronous mode interrupt OB
The data of the process image partition is updated synchronously to the assigned OB.
Isochronous mode interrupts give you the option of starting programs isochronously with
the backplane bus, with the PROFIBUS DP cycle or PROFINET send clock. Isochronous
mode interrupts are processed with high priority.
Setting the send clock or DP cycle time
The send clock/DP cycle time is the shortest possible transmission interval for the data
exchange. In isochronous mode, the send clock/DP cycle time corresponds to data cycle
T_DC.
For distributed I/O in S7-1500, you set the send clock in the properties of the CPU. For
PROFINET IO, you set the send clock in the properties of the PROFINET interface of the
CPU or in the sync domain. For PROFIBUS DP, you set the DP cycle time in the properties
of the DP master system.
Setting the application cycle
The application cycle is a multiple of data cycle T_DC. If the runtime of the isochronous
mode interrupt OB is short, the application cycle can be identical to the data cycle (= send
clock/DP cycle time).
You can reduce the application cycle of the isochronous mode interrupt OB relative to the
send clock of an isochronous system. Set an integer multiple of the send clock as the
reducing factor.
You use the factor to reduce the CPU utilization by executing the isochronous mode interrupt
OB less frequently. You set the application cycle in the properties of the isochronous mode
interrupt OB.
You can find more information in the section Programming isochronous mode (Page 43).
22
Isochronous mode
Function Manual, 10/2018, A5E43884988-AA
5