Isochronous Mode - Siemens SIMATIC S7-300 Manual

Analog modules
6.12 Analog output module SM 332; AO 4 x 16 bit; isochronous; (6ES7332-7ND02-0AB0)
6.12.3

Isochronous mode

Properties
Reproducible reaction times (i.e. of the same length) are achieved in a SIMATIC system by
means of a constant DP bus cycle, and synchronization of the single cyclic processes
outlined below:
● Cyclic user program execution. The length of the cycle time may vary due to acyclic
● Independent and variable DP cycle on the PROFIBUS subnet
● Cyclic operation of the backplane bus of the DP slave.
● Cyclic signal conditioning and conversion at the electronic modules of the DP slave.
The constant DP cycle runs in synchronism and at the same length. The CPU run levels
(OB61 to OB64) and isochronous IO are synchronized with this cycle. I/O data are therefore
transferred at defined and constant intervals (isochronous mode.) Maximum oscillation of
±50 μs.
Requirements
● The DP master and slave must support isochronous mode. You require
Mode of operation: Isochronous
Conditions of isochronous mode:
Processing and activation time T
transfer buffer and loading it into the D/A converter for output
T
DPmin
Diagnostic interrupt
6-114
program branching.
higher.
between reading the output value to the
WA
STEP 7
750 µs
1100 µs
max. 4 x T
DP
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
V5.2 or