Onboard Counter Inputs - Siemens SIMATIC S5-90U System Manual

S5-90U/S5-95U
11

Onboard Counter Inputs

The S5-90U is provided with a counter input which can optionally be used as digital input. The
S5-95U has two counter inputs which, however, cannot be used as digital inputs.
Table 11-1 gives an overview of the data of the counter and counter inputs.
Table 11-1. Characteristics of the Onboard Counter Inputs
Characteristics of the Counter Inputs
Number of counters
Counter frequency limit
Actual-value representation
Counter type
Input voltage for counter iputs
Programmer interface unassigned
*
Please refer to Sections 3.3.4 and 3.3.5 for counter input assignments.
Note
• The counters are active only when the PLC is in the RUN mode.
• The actual status of the counter is set to "0" at each transition from STOP to RUN.
• The actual status of the counter is not retentive.
Each time the PLC switched on, the actual status is set to "0".
• When connecting the supply voltage (load supply voltage) for the onboard outputs
and in the case of some I/O modules (451-8MA11, 482-8MA13 and 265-8MA01), a
pulse with a duration of approx. 100 µs is generated at the outputs. If these outputs
are used for controlling counter inputs, the count is thus incremented by "1". This
phenomenon is relevant only when the S5-90U or S5-95U are in the RUN mode.
The pulse has no effect on "standard inputs" which generally have longer input
delays.
Principle of Operation
• The counter input is routed to a (hardware) counter which operates independently of the CPU.
• The counter counts the signal edges present at the counter input. The onboard counter of the
S5-90U counts positive edges only. In the S5-95U, the user can parameterize whether positive
or negative edges are to be counted.
• The counter always needs a comparison value. When the actual counter status has reached the
comparison value, it is immediately reset to "0". After resetting, the counter immediately
resumes the counting of signal edges.
• Reaching of the comparison value triggers an interrupt, i.e. OB3 (see Section 9.1.2) is called
up. In order to enable you to determine the cause of the interrupt in OB3, the cause is flagged
in diagnostic byte IB 35 (see Chapter 5) when the program branches to OB3.
The principle of operation of the counter will be explained with an example on the following page.
EWA 4NEB 812 6115-02b
S5-90U
1
*
1 kHz
16-bit, fixed-point,
without sign
Up
24 V DC
Onboard Counter Inputs
S5-95U
2
*
2 kHz, 5 kHz
16-bit, fixed-point,
without sign
Up
24 V DC
11-1