iC-WG
14-BIT DIFFERENTIAL SCANNING OPTO ENCODER
Rev B0, Page 10/11
Control Monitor and Error Message Output
The error message output NERR is used to signal a possible incorrect scanning due to illuminances which are
too low or too high.
The control monitor observes the potential at the CSR pin. Voltages which bring the power driver to saturation
or off-state are recognized and indicated at the open collector output by NERR= low.
If the series resistor for the LED limits the transmit current, this is indicated at NERR. Due to the principle of
differential formation, however, the scanning is still guaranteed until the minimum brightness preset by the
hysteresis of the comparators is achieved. As the illuminance declines, the cut-off frequency will initially drop
without a faulty scanning developing in a static case (e.g. when code disk comes to standstill). Recognizing
such faulty scanning necessitates an additional evaluating logic which constantly checks the code (check for
unit-distance code in case of Gray code, parity check, etc.).
APPLICATIONS INFORMATION
Using the test aid
The threshold current defined in electrical characteristic No.602 must be exceeded at both pins TIP and TIN
simultaneously to activate the iC-WG’s built-in test aid. Once it has been activated, the test aid does not switch
back to off-state until the current drops below approx. 1µA.
A clamp circuit as shown in Figure 2 also prevents falling below the test aid turn-on threshold for a short time.
The output polarity of the iC-WG is to be changed over with the switch.
Figure 2: Wiring the test aid
ICHAUS [ IC-HAUS GMBH ]
