ST20-GP1 datasheet(13/116 Pages) STMICROELECTRONICS

13 / 116 page

ST20-GP1

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is maintained between the satellite one-millisecond epochs and the receiver, despite time-of-

reception variations due to the varying path length from the satellite.

Figure 3.2 DSP packet format

3.1

DSP module registers

The GPS hardware channels of the ST20-GP1 are controlled by three sets of registers:

DSPControl register

PRNcode0-11 and PRNphase0-11 registers

NCOfrequency0-11 and NCOphase0-11 registers

The base addresses for the DSP registers are given in the Memory Map chapter.

DSPControl register

The DSPControl register determines whether the PRN generators are on (normal use) or disabled

(for built-in-self-test of a system), whether the system is in tracking mode (840/970

µs output rate)

or initial acquisition mode (31/62

µs), and selects which of the two rates for each mode. It also

determines whether the accumulated carrier phase in the NCO are reset to zero automatically or

continue from their existing value. The bit allocations are given in Table 3.1.

62 byte packet every 840/970/31/62

µs

Absent 16-bit values padded with #8000

12 x 8-bit

time values

12 x 16-bit

Q values

12 x 16-bit

I values

16-bit

header

sync

sample

rate

Acquisition mode

First packet (in SV ms)

T[7:6] = 10

T[5:0] = time[5:0]

Remaining packets

T[7:6] = 00

T[5:0] = sequence number

(sequence numbers are 2 to

16 or 32)

Tracking mode

T[7:6] = 10

T[5:0] = time[5:0]

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