xe8802 Semtech Corporation, xe8802 Datasheet - Page 55

• Manufacturer Part Number: xe8802
• Description: Data Acquisition Soc With 16+10 Bit Zoomingadc? Embedded Risc Controller And Lcd Driver
• Manufacturer: Semtech Corporation

The oscillator characteristics are given in Table 7-11. The characteristics are valid only if the crystal and board
layout meet the specifications above.
Table 7-11. Crystal oscillator characteristics.
Note 1. This gives the relative frequency deviation from nominal for a crystal with CL=8.2pF and within the
temperature range -40°C to 85°C. The crystal tolerance, crystal aging and crystal temperature drift are not included
in this figure.
7.7
7.7.1
The user can provide an external clock instead of the internal oscillators. The external provided frequency is
internally divided by two. The external clock input pin is XIN.
The system is configured for external clock by bit EnExtClock in register RegSysClock. Using the bits in the
registers RegSysRcTrim1 and RegSysRcTrim2, the ck32kHz clock frequency can be controlled (see section
7.10).
Note: when using the external clock, the Xtal is not available.
7.7.2
The external clock has to satisfy the specifications in the table below. Correct behavior of the circuit can not be
guaranteed if the external clock signal does not respect the specifications below.
Table 7-12. External clock specifications.
Note 1. For VBAT≥2.4V
Note 2. For VBAT=VREG=1.2V
7.8
There are three possible clock sources available for the CPU clock. The RC clock is always selected after power-
up, a negative pulse on NRESET or after Sleep mode. The CPU clock selection is done with the bit CpuSel in
RegSysClock (0= fastest clock, 1= 32 kHz from Xtal if EnableXtal =1 and EnExtClock = 0 else from high
prescaler 32 kHz output).
Switching from one clock source to another is glitch free.
© Semtech 2006
Symbol
f
St_xtal
Fstab
Symbol
F
PW_1
PW_0
F
PW_1_LV
PW_0_LV
Xtal
EXT
EXT_LV
External clock
Clock source selection
External clock configuration
External clock specification
Description
Nominal frequency
Start-up time
Frequency deviation
Description
External clock
frequency
Pulse 1 width
Pulse 0 width
External clock
frequency
Pulse 1 width
Pulse 0 width
XE8802 Sensing Machine Data Acquisition MCU
-100
0.06
0.03
TBD
TBD
Min
Min
32768
Typ
Typ
1
7-8
with ZoomingADC™ and LCD driver
TBD
Max
Max
300
20
20
2
8
Unit
Hz
s
ppm
Unit
MHz
µs
µs
kHz
µs
µs
Comments
Note 1
Comments
Note 1
Note 1
Note 1
Note 2
Note 2
Note 2
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