Siemens SIMATIC S7-300 Manual page 317

Cycle time of module in 8-channel mode
The channel conversion time, including module communication time, is 84 ms. After this
cycle, the module has to change over to the second channel of the group using OptoMOS
relays. Opto-MOS relays require switching and settling times of 12 ms. Each channel
requires a time of 97 ms, i.e. the total cycle time equals 194 ms.
Cycle time = (t
Cycle time = (84 ms + 16 ms) x 2
Total cycle time = 200 ms
t : Conversion time for one channel
C
t : Channel changeover time within the channel group
C
8-channel mode (software filter)
Analog-to-digital conversion in this mode is identical to the conversion in 8-channel mode
(hardware filter). The four analog-to-digital converters (ADC) of the module simultaneously
convert channels 0, 2, 4 and 6. The ADCs first convert the channels with even numbers,
then those with the odd numbers 1, 3, 5 and 7 (see the figure below.)
Figure 6-24
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
6.9 Analog input module SM 331; AI 8 x RTD; (6ES7331-7PF01-0AB0)
+ t ) x 2
K U
8-channel mode cycle time (software filter)
Analog modules
6-83