ST20-GP1 datasheet(15/116 Pages) STMICROELECTRONICS

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ST20-GP1

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For channels 0 and 1, RTCA-SC159 satellite codes can also be selected. This is achieved by

setting the PRNcode0-11 register appropriately and also writing the initial value for the satellite to

the PRNinitialVal0-1 register, see Table 3.8. If uninitialized by the software, the PRNinitialVal

The PRNcode0-11 and PRNinitialVal0-1 registers are normally written only when the satellite is

ﬁrst chosen.

PRNphase0-11 registers

The PRN0-11phase registers determine the relative delay between the receiver master clock, and

the start of the one millisecond repetitive code sequence. The code sequence starts when the

receiver clock counter (invisible to the software except through message timestamps) reaches the

value written to the PRNphase0-11 register. The PRNphase0-11 register must only be written

once per satellite milliseconds-epoch, which varies from the receiver epoch dynamically due to

satellite motion. Synchronism with the software is achieved by reading the register, when a write

enable ﬂag is returned. If not enabled, the write operation is abandoned by the software.

a. Refer to the US DoD document ICD-GPS-200.

b. It is the responsibility of the software to ensure that when this value is selected, a suitable value has

been written into the PRNinitialVal0-1 register. If this channel is later used for a standard GPS sat-

ellite, the PRNinitialVal0-1 must be set to all ones (#3FF).

#29

#41

#52

#63

#74

#05

#16

#31

#64

#75

#06

#17

#28

#61

#72

#03

#14

#25

#24

#71

#02

#24

WAASb

#20

Satellite ID

PRNcode0-11

Taps selected from G2 shift registera

by bits 6 to 4

by bits 3 to 0

Table 3.3 PRNcode0-11 register value

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