Siemens SIMATIC S7-300 FM 350-1, Manual

Page: 87 / 198

Operating Modes, parameters and commands
7.3 Count modes
FM 350-1 Counter module
Manual, 05/2011, A5E03648639-01
87
7.3.2 Basic principles
Load value
The load value is the counter level from which the FM 350-1 starts the counting process.
You can assign a load value LOAD_VAL to the FM 350-1 during operation. This will
overwrite the starting count.
You can assign this load value directly (control signal L_DIRECT). It is then accepted directly
by the FM 350-1 as a new counter value and loaded in preparation.
You can load the load value in preparation only (control signal L_PREPAR). A load value
that is loaded in preparation is accepted by the FM 350-1 as a new counter value in
response to the following events:
●
In the single counting and periodic counting modes
–
When the high or low count limit is reached if no main count direction is set.
– When the set high count limit is reached with main count direction up.
– When 0 is reached with main count direction down.
● In all counting modes
–
The counting process is started by the canceling SW or HW gate (the load value is not
accepted when the counting continues).
– Synchronization
– Latch/retrigger
Gate control
You can use the hardware gate (HW gate) and software gate (SW gate) to control the
FM 350-1 counting processes, meaning to start and stop them.
Maximum Count Range without Main Count Direction
The 32-bit binary counter of the FM 350-1 can work in two different modes, depending on the
parameterization.
Table 7- 2 Modes for the 32-bit binary counter of the FM 350-1, depending on the parameterization
Count range "0 to +32-bit"
(32-bit unsigned) Count range "–31 to +31-bit"
(31-bit signed)
Decimal count
range
0 to +4 294 967 295 -2 147 483 648 to +2 147 483 647
0000 0000 to FFFF FFFF 8000 0000 to 7FFF FFFF Hexadecimal
count range
An overflow is detected when the
counter value (hexadecimal) changes
from FFFF FFFF to 0, and an
underflow is detected when it changes
from 0 to FFFF FFFF.
An overflow is detected when the counter
value (hexadecimal) changes from
7FFF FFFF to 8000 0000, and an
underflow is detected when it changes
from 8000 0000 to 7FFF FFFF.