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3.11 Checksum Filed
This absolute value is calculated by exclusive OR operation on 8 data bits (ASCII code) (no start or stop bits) of each
character in the message, between, but excluding "$" and "*" (or between "#" and "*") characters. The hexadecimal
value of the most significant and the least significant 4 bits of the result is converted to two ASCII characters (0-9, A-F)
for transmission. The most significant character is transmitted first
3.12 Warning and Alarm Settings
Tilt and magnetometer limits can be programmed in to the EERROM to generate Warning and Alarm conditions in the
status fields of the HPR sentence output.
Tilt Settings
When the tilt measured is below the warning level, the status fields will indicate 'N'.
$PTNTHPR,59.6,N,-0.2,N,-3.0,N*0F
Tilt high warning and high alarm can be user programmed.
When the pitch or roll measured is between the warning and alarm levels, the HPR message will indicate this with letter
'O' in the corresponding pitch or roll status field.
$PTNTHPR,72.9,N,-1.6,N,-29.6,O*33
When the pitch or roll measured is beyond the alarm level, the HPR message will indicate this with letter 'P' in the
corresponding pitch or roll status field, and the heading field will be null.
$PTNTHPR,,N,-1.5,N,,P*03
Magnetometer Settings
Four levels can be set for the magnetometer alarm and warning levels. High Warn and Alarm levels, and Low Alarm and
Warning levels. Five settings are generated depending on the measured total magnetic field value (Mag T) and the levels
programmed in the EEPROM.
Level
Low Warn < Mag T < High Warn
High Warn < Mag T < High Alarm
High Alarm < Mag T
Low Alarm < Mag T < Low Warn
Table 4. Relationaship between the Mag total measured and the mag status field
Mag T < Low Alarm
Magnetometer high alarm condition example
$PTNTHPR,,P,0.3,N,0.1,N*06
900240 Rev. B
Mag Status Field
N
O
P
M
L
3/01
Heading Field
normal
normal
Null
normal
Null
page 13
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