User Manual

PD28-1-1021 / PD28-3-1021 V1.4 Hardware Manual (Rev. 1.03 / 2018-JAN-25) 15
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The inputs are protected using voltage resistor dividers together with limiting diodes against voltages
below 0V (GND) and above +3.3V DC. The circuit of the two outputs and the two inputs connected in
parallel to the inputs is shown below:
VDD
OUT_0 / IN_2
OUT_1 / IN_3
microcontroller
GND
+3.3V
microcontroller
10k
10k
1nF
GND
GND GND
1k
GND
since V1.4
Figure 3.8 General purpose outputs OUT_0, OUT_1 and inputs IN_2, IN_3 connected in parallel
The outputs of the N-channel MOSFET transistors (Open-Drain) are connected to freewheeling diodes each
for protection against voltage spikes especially from inductive loads (relais etc.). Please take into account
the 20k (2x 10k in series) resistance to ground (transistor not active) of the input voltage divider (figure
4.8) when designing the external “load” circuit.
Since hardware version 1.4 the gate inputs of the MOSFETs are pulled-low during power-up and while the
processor might be still in reset / output pins not initialized. This way, the outputs will not briefly switch
on at power-up.
The two outputs OUT_0 / OUT_1 and inputs IN_2 / IN_3 have alternate functions depending on configuration
in software:
Label
(connector pin)
Default Function
Alternate function 1
Alternate function 2
OUT_0 / IN_2 (7)
Open drain output with
freewheeling diode (max.
100mA)
Please note: there is a 20k
pull-down resistor of the
input connected in parallel
Alternate function 1: general
purpose digital input,
+24V compatible, internal
20k pull-down resistor
Alternate function 2:
home switch, +24V
compatible, internal 20k
pull-down resistor
OUT_1 / IN_3 (8)
Open drain output with
freewheeling diode (max.
100mA)
Please note: there is a 20k
pull-down resistor of the
input connected in parallel
Alternate function 1:
digital input, +24V
compatible, internal 20k
pull-down resistor
Alternate function 2:
analog input, 0..6.6V range,
+24V survival, internal 20k
pull-down resistor
Table 3.4 Multipurpose outputs / inputs / alternate functions
Do not apply any voltage above supply voltage to inputs IN_2 and IN_3. Due to the
freewheeling diodes of the outputs connected in parallel they will be shorted to power supply
input voltage.