Siemens ISI EN 50295 Brochure page 98

AS-Interface Slaves
Modules with special functions
Counter modules
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Overview
This module is used to transfer hexadecimal coded counter val-
ues (LSB=D0, MSB=D3) to a higher-level controller. Each valid
count pulse on terminal 8 causes the counter value to be incre-
mented. The module counts from 0 up to 15 and then starts
again at 0. The control system then loads the current value and
determines the number of pulses between two host calls by gen-
erating the difference. The total number of counter pulses is de-
termined by summation of these differences.
To ensure that valid values are transferred, no more than 15
count values must be applied to terminal 8 between two host or
ASI master calls. The maximum permissible transfer frequency
is calculated as follows from these times:
f = 15 / T
Tmax max
T : Maximum possible transfer time from slave to host.
max
Another restriction on the maximum frequency is the required
pulse shape. To ensure that the counter loads a pulse as valid,
a low value must be applied to the input for at least 300 µs, while
a high value must be applied for at least 1 ms. This results in a
maximum frequency for the counter module independent of the
controller of
f = 1 / 1.3 ms = 769 Hz for the counter module
FCmax
(see diagram nsa00084).
6
In the event of non-compliance with the time criterion shown in
the adjacent diagram, the counter value is rejected.
The counter is only active for the reset parameter P2 (default). By
setting P2, the counter is erased, but incoming pulses are only
registered when P2 has been reset.
Note:
A customer-specific function block is required
or must be programmed.
6/98 Siemens IK PI · 2004
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Typical connections