ST20-GP1 datasheet(16/116 Pages) STMICROELECTRONICS

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ST20-GP1

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The 19-bit value comprises three ﬁelds. The 3 least signiﬁcant bits represent the fractional-delay in

eighths of a code-chip. The middle 10 bits represent the integer delay in code-chips, 0-1022, with

the value 1023 illegal. The upper 6 most signiﬁcant bits represent the delay in integer milliseconds.

Note also that the eighth-chip resolution of the code generator is not sufﬁcient for positioning. At

125 ns it represents approximately 40 m of range, over 100 m of position. The software must

maintain the range measurements around the 1 ns resolution level in a 32-bit ﬁeld, and send an

appropriate 19-bit sub-ﬁeld to the register. Note, care must be taken when calculating this ﬁeld from

a computed delay, or vice versa, to allow for the missing value 1023. The overall register bit-ﬁeld

cannot be used mathematically as a single binary number.

PRNphase0-11WrEn registers

The PRNphase0-11WrEn ﬂags are active low ﬂags that record when the PRNphase0-11 register

can be updated. The PRNphaseWrEn ﬂag for a channel is set high when the corresponding

PRNphase register is written. The ﬂag is reset again when the value written is loaded into the PRN

generator. Note, the PRNphase0-11 register should only be updated when the PRNphase0-

11WrEn register has been cleared by the hardware.

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

represents

264KHz/(218),

i.e.

1.007080078125 Hz.

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

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

PRNphase0-11

DSP base address + #40 to #6C

Write only

Bit

Bit ﬁeld

Function

2:0

FractionalDelay

Fractional delay in eighths of a code-chip.

12:3

IntegerDelay

Integer delay in code-chips. Value 0-1022. Note, the value 1023 is illegal.

18:13

Delay

Delay in integer milliseconds.

Table 3.4 PRNphase0-11 register format

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

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