Siemens S7-300 appendix Different cycle times, Extension of the cycle time due to error

Cycle and reaction times 5.2 Cycle time

Extension of the cycle time due to error

Table 5-8	Cycle time extension as a result of errors
Type of error		Programming errors	I/O access errors
312C		600 μs	600 μs
313C		400 μs	400 μs
313C2		400 μs	400 μs
314C-2		400 μs	400 μs
312		600 μs	600 μs
314		400 μs	400 μs
315		400 μs	400 μs
317		100 μs	100 μs

The interrupt OB processing time must be added to this extended time. The times required for multiple nested interrupt/error OBs are added accordingly.

5.2.3Different cycle times

Overview

The cycle time (Tcyc) length is not the same in every cycle. The figure below shows different cycle times Tcyc1 and Tcyc2. Tcyc2 is longer than Tcyc1, because the cyclically executed OB1 is interrupted by a time-of-day interrupt OB (here: OB 10).

Current cycle	Next cycle	Cycle after next
Tcyc 1	T cyc 2
	OB10

Updating Updating

PIO PII

OB1 CCP

Updating	Updating
PIO	PII	OB1	OB1 CCP

Updating Updating

PIO PII

Block processing times may fluctuate

Fluctuation of the block processing time (e.g. OB 1) may also be a factor causing cycle time fluctuation, due to:

•conditional instructions,

•conditional block calls,

•different program paths,

•loops etc.

5-8	CPU 31xC and CPU 31x, Technical data
	Manual, Edition 08/2004, A5E00105475-05