ST20-GP6 datasheet(17/123 Pages) STMICROELECTRONICS

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ST20-GP6

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erator. Note, the

PRNphase0-11 register should only be updated when the PRNphase0-11WrEn

NCOfrequency0-11 registers

The

NCOfrequency0-11 registers hold a signed 18-bit value that is added repetitively, ignoring

overﬂows, to the accumulated NCO phase from which the NCO sine and cosine waveforms are

generated. The addition is performed at a 264 KHz rate (16.368MHz/62). The accumulated NCO

phase is not accessible to the software, but can be cleared when initialising the channel if enabled

by the

DSPControl register.

Each

unit

value

the

NCOfrequency0-11 register represents 264KHz/(218), i.e.

1.007080078125 Hz.

If the extreme values are written, #1FFFF and #20000, the sine wave generated will be at approxi-

mately +132 KHz, and precisely -132 KHz respectively.

NCOphase0-11 registers

The

NCOphase0-11 registers contents are added to the accumulated phase to correct the carrier

for the ﬁnal 1 Hz that cannot be resolved by the NCO frequency. This addition is not cumulative,

and the value must be updated regularly by the software as a result of carrier phase errors mea-

sured on the satellite signal. The register holds a signed 7-bit ﬁeld representing +/-180 degrees

total in steps of 2.8125 degrees (360/128).

PRNphase0-11WrEn

DSP base address + #40 to #6C

Read only

Bit

Bit ﬁeld

Function

PRNphaseWrEn

Set when the corresponding

PRNphase0-11 register is set.

Table 3.5

PRNphase0-11WrEn register format

NCOfrequency0-11

DSP base address + #80 to #AC

Write only

Bit

Bit ﬁeld

Function

17:0

NCOfrequency

NCO frequency as a signed 18-bit value.

Table 3.6

NCOfrequency0-11 register format

NCOphase0-11

DSP base address + #C4 to #EC

Write only

Bit

Bit ﬁeld

Function

6:0

NCOphase

NCO phase as a signed 7-bit value representing +/-180 degrees total in steps of

2.8125 degrees (360/128).

Table 3.7

NCOphase0-11 register format

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