Siemens simatic s7-400 FM 450-1, Руководство пользователя, Страница: 75 / 130

Modes, settings, parameters and commands
8.12 Initiating a process interrupt
Counter module FM 450-1
Manual, 02/2014, A5E03648739-02
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8.7 Count range
Introduction
There is a 32°bit-wide count register on the module. With the count range you specify if the
module counts only in the positive range or if the 32nd°bit is interpreted as a sign bit and
hence negative numbers can be represented. This section describes these two count
ranges, "0 to +32 bits" and "-31 to +31 bits".
Count ranges
The FM 450-1 counts within different limits in the count ranges 0 to +32 bits and -31 to
+31 bits. In each case an overflow or an underflow is identified at the range limits.
In the "-31 to +31 bits" count mode, the counter status is represented in the two's
complement.
Count range Overflow Underflow
0 to +32 bits
1)
0 to 4 294 967 295 0 to
FFFF FFFFH
When the counter status changes
from 4 294 967 295 to 0
When the counter status changes from
0°to 4 294 967 295
-31 to +31 bit -2 147 483 648 to
2 147 483 647
8000 0000H to
7FFF FFFFH
When the counter status changes
from +2 147 483 647 to -
2 147 483 648
When the counter status changes from
-2 147 483 648 to +2 147 483 647
1)
In this count range, you can only specify and evaluate values in hexadecimal.
Overflow, underflow and zero crossing
A bit is set in the DB of FC°CNT_CTRL for both count limits in the case of overflow and
underflow (see section "Assignment of the DB (Page 103)").
In the "-31 to +31 bit" count range, a bit is similarly set in the DB on a zero crossing.
In the "0 to +32 bit" count range, an overflow or underflow, depending on the direction of
counting, is additionally indicated on a zero crossing.
Event Bit in the DB
Overflow STS_OFLW is set
Underflow STS_UFLW is set
Zero crossing STS_ZERO is set
Triggering hardware interrupts
You can also signalize the events overflow, underflow and zero crossing by means of
hardware interrupts.