ams Datasheet Page 11
[v1-00] 2015-Apr-01 Document Feedback
HLS-440P − Electrical Interface
Byte 7 Safety Byte CRC
Figure 15:
Byte 7 Safety Byte Order
The CRC byte shows the 7-bit CRC over byte 0-6 with the
Polynomial 0xE5.
PWM
This section describes the PWM output that is available in some
variants of HLS-440P.
Physical Interface
The electrical connector is the same as in the variants with CAN
bus interface (see Electrical Connector ). Type A has a
termination resistor while type B does not.
The PWM signal is created as a differential CAN signal on pin 3
and 4. A CAN signal is said to be in a dominant state when the
signal lines are separated (a dominant bit is transmitted). When
the signal lines are at the same voltage level, the state is
recessive. Recommended circuitry to convert CAN signals to
TTL is specified in a separate document, available on request.
The PWM signal is only an output signal. No other transmitting
devices should be attached to the bus.
The PWM Signal
The PWM signal has a period time of 255 μs. The rather short
period is chosen since modern CAN transceivers do not allow
for a longer dominant state.
The duration of the recessive state can be translated into output
H
2
prediction from the sensor module. The recessive duration
(pulse width) ranges from 20 to 220 μs, which corresponds to 0
to 10% hydrogen. An error is shown as a 10 μs pulse width. At
startup the pulse width will be 255 μs (100% duty cycle) until
the first valid H
2
concentration is delivered after 5 s.
The figure below shows the output for 0% hydrogen (pulse
width of 20 μs).
Bit
MSB
7
6 5 4 3 2 1
LSB
0
Byte 7 XXXXXXXX
