GP2021
SOURCESEL, bit 10: Selects which input source to be
used by the channel when in Real_lnput mode. Low selects
SIGN0 and MAG0, high selects SIGN1 and MAG1.
After a master reset (NRESET low), GPS mode is selected,
but with all zeros in the G2 generator, the G1 code is seen
at the output of the C/A code generator.
MEAS_STATUS_A (Read address)
CODE_OFF/ONB, bit 11: When low, the code is output
normally, but when high, the Prompt, Early and Late codes
are held high (code mixer outputs exactly follow inputs)
and the Early-minus-late code is held low. This is intended
for test purposes only.
Bit
Bit name
15 to 14 Not used
13
12
11
10
9
8
7
6
5
4
3
2
1
TIC
MEAS_INT
CH11_MISSED_MEAS_DATA
CH10_MISSED_MEAS_DATA
CH9_MISSED_MEAS_DATA
CH8_MISSED_MEAS_DATA
CH7_MISSED_MEAS_DATA
CH6_MISSED_MEAS_DATA
CH5_MISSED_MEAS_DATA
CH4_MISSED_MEAS_DATA
CH3_MISSED_MEAS_DATA
CH2_MISSED_MEAS_DATA
CH1_MISSED_MEAS_DATA
CH0_MISSED_MEAS_DATA
Table 20
PRESET/UPDATEB, bit 12: When high sets the channel
into Preset mode, or when low, sets the channel into Update
mode. This bit is cleared to low after the Preset function
has been performed, that is, after the first TIC following
the loading of the Epoch counters.
TRACK_SEL (1 and 0), bits 14 and 13: Select the
appropriate code to be produced by the Tracking arm
output of the code generator as shown in Table 19.
Bit
Code select
0
14
13
0
0
1
1
0
1
0
1
Early code
Late code
Dithering code (alternating early and late)
Early-minus-late code
CHx_MISSED_MEAS_DATA status bit, when high,
indicates that one or more sets of measurement data have
been missed since the last read from this register. It is set
high by a read from the Code Phase Counter of the same
channel, when the previous value in the Code Phase
Counter has not been read, and is reset by a read from
the MEAS_STATUS_A register or by disabling the channel.
Table 19 TRACK_SEL bit settings for Tracking arm
code selection
When the dithering code has been selected, the Tracking
arm will use the Early code for 20 periods of the Gold code,
the Late code for the next 20 periods and then this process
of alternating between Early and Late code will be repeated
indefinitely. The Tracking Arm will toggle between Early or
Late codes on every increment of a 20ms Epoch Count.
Its state can be determined by reading the
ACCUM_STATUS_C register.
If this register is always read after the Code Phase Counter,
it indicates whether measurement data has been missed
before the last read of the Code Phase Counter. All
CHx_MISSED_MEAS_DATA bits are set low by a
hardware (NRESET) or software (MRB reset.
The output code is a sequence of 11s and 21s for all
code types except EARLY-MINUS-LATE where the result
can also be a 0. In EARLY-MINUS-LATE mode the values
are not the 12, 0, 22 that result from the calculation (11
or 21) 2 (11 or 21), but are halved to 11, 0, 21. This
must be considered when choosing thresholds in the
software as the correlation results will be exactly half the
values otherwise expected.
The MEAS_INT bitis set high at each TIC and 50ms before
each TIC (ifTIC period is greater then 50ms), and is cleared
by reading this register. This bit is used as a flag to the
microprocessor to time software module swapping and is
reset by a hardware master reset (NRESET low) but not
by an MRB software reset.
The TIC bit is set high at every TIC and is cleared by
reading this register. The purpose of the bit is to tell the
microprocessor that new Measurement Data is available.
This bit is reset by a hardware master reset (NRESET at
low) but not by an MRB in RESET_CONTROL.
GPS_NGLON, bit 15: Setting this bit to low changes the
C/A code generator mode to GLONASS mode, to generate
the fixed 511-bit sequence used by all GLONASS satellites.
37
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