st20-gp1 STMicroelectronics, st20-gp1 Datasheet - Page 16

• Manufacturer Part Number: st20-gp1
• Description: Gps Processor
• Manufacturer: STMicroelectronics

ST20-GP1
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
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.
16/116
PRNphase0-11
Bit
2:0
12:3
18:13
PRNphase0-11WrEn
Bit
0
NCOfrequency0-11
Bit
17:0
unit
Bit field
FractionalDelay
IntegerDelay
Delay
Bit field
PRNphaseWrEn
Bit field
NCOfrequency
value
DSP base address + #40 to #6C
DSP base address + #40 to #6C
DSP base address + #80 to #AC
in
Table 3.5 PRNphase0-11WrEn register format
Table 3.6 NCOfrequency0-11 register format
the
Function
Fractional delay in eighths of a code-chip.
Integer delay in code-chips. Value 0-1022. Note, the value 1023 is illegal.
Delay in integer milliseconds.
Function
Set when the corresponding PRNphase0-11 register is set.
Function
NCO frequency as a signed 18-bit value.
Table 3.4 PRNphase0-11 register format
NCOfrequency0-11
register
represents
264KHz/(2
Write only
Read only
Write only
18
),
i.e.