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HLS-442

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
ams Datasheet Page 7
[v1-00] 2015-Mar-30 Document Feedback
HLS-442 − Electrical Interface
Messages From the Sensor
The main message sent from the sensor to the control unit is
the Sensor Status Message, hereafter referred to as the SSM.
After 700 ms from power-ON of the sensor it will start sending
the SSM frame as defined below. The SSM, after this event, is
transmitted periodically with a 100 ms interval until the sensor
is powered OFF. Besides the SSM, the sensor can also send a
Wake-Up pulse. This is described in detail in Wake-Up Function.
The Wake-Up pulse is separate from the SSM and has no impact
on the SSM.
The figure below defines the data field of the SSM CAN data
frame. The data field uses 8 bytes. The CAN ID as described
earlier sets the arbitration field.
Figure 8:
CAN Matrix Message Layout
Parameter
Name
Data
Size
Physical
Measurement
Range
Value
Range
b7 b6 b5 b4 b3 b2 b1 b0
Byte
No.
H
2
Concentration
8 bits 0 – 4.4 % [20 -240]
H
2
Concentration
0
Protection
Value 1
8 bits pv1 1
FE high 8 bits FE high 2
CRC16 Byte 1
(Higher Byte)
8 bits CRC16 3
FE low 2 bits FE low
0
4
Protection
Value 2
2 bits pv2 4
Sensor
Number
3 bits [1 - 7]
UB
2
UB
1
UB
0
4
Msg. Counter 8 bits [0 - 255] Msg Counter 5
Sensor status 2 bits [0 - 3] status 0 6
Part number 5 bits [1 - 31] Part number 0 6
CRC16 Byte 2
(Lower Byte)
8 bits CRC16 7
Page 8 ams Datasheet
Document Feedback [v1-00] 2015-Mar-30
HLS-442 − Electrical I nterface
H
2
Concentration
0% is encoded with decimal number 20.
4.4% (44000 ppm) is encoded with decimal number 240.
The relation between detected H
2
concentration (in ppm) and
concentration code as signaled in the message is:
Code = round(H
2
/200) + 20
H
2
= (code – 20)*200
Where round() denotes rounding towards the nearest integer.
Protection Value
The protection value offers a 10-bit consistency check of the
transmitted concentration, status and message counter. The
following pseudo code describes the algorithm forming the
10-bit value and how it is projected on to the protection value
1 and the protection value 2 bytes in the SSM.
code[7 - 0] denotes the set of 8 bits transmitted as code for
representing the H
2
concentration.
status[1 - 0] denotes the set of two bits transmitted as code for
representing sensor status.
mgscnt[6 - 0] denotes the set of 7 bits transmitted as code for
representing message counter.
pv[9 - 0] denotes the set of 10 bits forming the protection value.
pv1[7 - 0] denotes the set of 8 bits transmitted as code for
protection value 1.
pv2[1 - 0] denotes the set of 2 bits transmitted as code for
protection value 2.
(EQ1)
(EQ2)
ams Datasheet Page 9
[v1-00] 2015-Mar-30 Document Feedback
HLS-442 − Electrical Interface
Figure 9:
Pseudo Code Description of Protection Value
FE High / FE Low
The raw FE signal is available in 10-bit resolution (1 step = 4mV).
The high 8 bits are available in byte 2 and the lower 2 bits in
byte 7, bit 6-7. The data range is 0-4092mV.
CRC16
Byte 3 and byte 7 form a 16-bit CRC value. The CRC is CCITT
CRC16.
Sensor Number
Sensor Number is defined by power supply feeds and CAN ID
assigned sensor number is repeated in byte 4 bit 2-4. The value
sent is given in Bus Identification.
Message Counter
The message counter is incremented by 1 after each
transmission of a SSM frame. After the counter reaches 255 it
wraps around and the next transmitted counter value
becomes 0. At sensor start-up the message counter begins at 1.
Pseudo Code Description
pv[9 - 8] = status[1 - 0] Assign two most significant bits of pv as the status bits
pv[7 - 0] = code[7 - 0] Assign 8 least significant bits of pv as the code bits
pv[9 - 0] = pv[9 - 0] +
msgcnt[1 - 0]
To pv add the number formed by two least significant bits of the message
counter
pv[9 - 0] = NOT pv[9 - 0] Perform bitwise inverse of pv
pv[9 - 0] = pv[9 - 0] + 1 To pv add 1
pv1[7 - 0] = pv[7 - 0]
Form protection value 1 of the 8 least significant bits of the 10-bit
protection value
pv2[1 - 0] = pv[9 - 8]
Form protection value 2 of the 2 most significant bits of the 10-bit
protection value
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

HLS-442

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