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XLi Time & Frequency System
XLi-man, Issue 8, 6/17/2008, Rev. H
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The transmission is initiated on a time mark, so that the first bit of the 400 “ones” starts within 10
microseconds of the leading edge of the 1PPS.
The start of message indicator that follows the “ones”, verifies that the time, day of year, year and TFOM
message will follow. Each 8 bit character in the data message (time of day, day of year, year and TFOM)
is defined by a modified 8:4 Hamming Code. The two start-of-message characters, (8 bits each) are not
in the modified Hamming Code.
The modified Hamming code employs 4 parity bits and 4 data bits for each 8 bit character.
The Time Figure of Merit TFOM denotes the time quality of the incoming Have Quick code. While the Xli
is locked all bits are high (indicating no information), no fault is reported. When the time error in the Xli
exceeds 10mSec the bits are set to an integer value of 9 (indicating time error of 10mS or fault). Other
equipment such as the Xli with Have Quick input will read the TFOM and unlock.
Refer to ICD-GPS-060 Rev A section 4.4.5 for the Have Quick interface requirements.
HaveQuick without TFOM Output:
Signal characteristics
The Have Quick signal employs biphase (Manchester II) transmission at approximately 1667 bits per
second. A logical one is defined as 300 microseconds of a low state followed by 300 microseconds of a
high state. A transmission of 240 milliseconds of logic ones (400 bits) precedes the start of message
indicator (16 bits) and time, day of year, and year message (88 bits as opposed to 96 with TFOM).
The transmission is initiated on a time mark, so that the first bit of the 400 “ones” starts within 10
microseconds of the leading edge of the 1PPS.
The start of message indicator that follows the “ones”, verifies that the time, day of year, and year
message will follow. Each 8 bit character in the data message (time of day, day of year, and year) is
defined by a modified 8:4 Hamming Code. The two start-of-message characters (8 bits each) are not in
the modified Hamming Code.
The modified Hamming code employs 4 parity bits and 4 data bits for each 8 bit character.
Refer to ICD-GPS-060 Rev A section 4.4.5 for the Have Quick interface requirements.
Electrical characteristics
Qty:
4
Connector:
BNC female
Physical:
Single high option bay
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