st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 74

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

ST20-GP6
The SysRatio register, see Table 11.8 on page 69, gives the speed at which the system PLL is
running. It contains the relevant PLL multiply ratio when using the PLL, or contains the value ‘1’
when in TimesOneMode for the PLL.
13.3.2 Clocking sources
The real time clock and low power timer and alarm must be clocked at all times by one of the following
clocking sources:
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External clock input (LowPowerClockIn) — this clock must not be more than one eighth of
the system clock rate. In this case the LowPowerClockOsc pin should not be connected
on the board.
Watch crystal, as in Figure 13.1.
SpeedSelect1
a. In TimesOneMode the PLL is disabled to reduce power consumption.
A - this node should have very low capacitance < 10 pF.
B - this node must have zero dc load.
LowPowerClockIn
0
0
1
1
10 pF
SpeedSelect0
GND
Figure 13.1 Watch crystal clocking source
B
Table 13.1 Processor speed selection
0
1
0
1
watch crystal
(32768 Hz)
Processor clock
speed (MHz)
16.368
32.736
49.104
A
GND
330 K
22 pF
LowPowerClockOsc
cycle time (ns)
approximate
RESERVED
Processor
61.1
30.5
20.4
internal low power clock
Phase lock loop
TimesOneMode
factor (PLLx)
2
3
a