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DPC31 HW

Page 60 Version V 1.0

DPC31 HW Description

The leading edge of each arriving pulse (2) triggers a timer with the run time t3. The following condition with

regard to time applies:

t1 < t3 < t2

. When t3 expires, the pulse length on t1 and t2 is polled. Depending on

the pulse duration t1 or t2 that was detected respectively, the flipflop FF1 is set to L or H. The output of the

flipflop thus corresponds to the serial data signal RxS1 (4). The output signal (5) of an additional flipflop FF2

is combined with the signal (4) via an or function. When 2 short pulses arrive consecutively, both flipflops are

reset. The or-function results in an L, which is recognized as the end of the static signal RxE1 (6). With the

signal (7), an additional retriggerable timer t4 (40 µs ≤ t4 ≤ 100 µs) resets the two evaluation flipflops during

transmission pauses in order to suppress undefined setting through interference signals.

Pulses of < 0.5 µs that are pending at the comparator output are reliably suppressed; pulses ≥ 1 µs are

reliably detected.

Alternative Suggestion regarding Comparator Circuitry:

The wiring of the comparator output described under Figure 7.5-9 has the disadvantage that the comparator

has to be supplied with the external voltage 5V via the input V

, and a level adaptation is necessary at the

output. In addition, a control area up to the positive supply voltage has to be ensured. The circuit variant

below (Figure 7.5-11) avoids these disadvantages. The two voltage dividers R2 / R3 and R4 / R5 move the

work area of the comparator to the center of the internal supply voltage V

; an offset results from the

difference of the values R2 and R4 in the idle state; R6 causes a decrease in amplitude; C2 a delay of the

reference voltage in the active circuit state. The capacitor C1 decouples the external voltage 5V and the

internal V

. This comparator circuit is not integrated into the DPC31 and must be implemented externally.

RxS_IM

anal.

Figure 7.5-11: Wiring of the Comparator with Bridge Network

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Siemens SPC3 Dokumentacja Strona 62