xe1205 Semtech Corporation, xe1205 Datasheet - Page 39

• Manufacturer Part Number: xe1205
• Description: Low-power, High Link Budget Integrated Uhf Transceiver
• Manufacturer: Semtech Corporation

specification. OSCParam_Resxosc(3:0) is set to 0000 by default, which selects a parallel resistor of 3.8 MW. This
default value is used with a 39 MHz crystal enabled on its fundamental frequency.
In the case of overtone operation where the microcontroller uses the XE1205 as a clock source, the user should note
that during the power up sequence of the XE1205, the oscillator may start and run at its fundamental frequency until the
correct value of parallel resistor in the register OSCParam_Resxosc(3:0) is programmed. Before time-sensitive
operations an oscillator settling period should be observed to ensure the desired oscillation frequency.
When OSCParam_Clkout is set high, a CLKOUT clock frequency is provided for a microcontroller or external circuitry. A
user-programmable frequency divider ratio of 2, 4, 8, 16, 32 is selectable depending on OSCParam_Clkout_freq(2:0).
The input frequency of this divider is the 39.0 MHz reference clock; the possible output frequencies are listed in Table
27:
When the XE1205 is in sleep mode, CLKOUT is inactive even if bit OSCParam_Clkout remains high.
The internally generated power on reset signal sets the MCParam, RXParam, and TXParam registers to
exception is the CLKOUT generation: though OSCParam_Clkout is set to low (i.e. disabled) the XE1205 provides a
signal at 1.22 MHz on the pin CLKOUT.
The first rising edge on the NSS_CONFIG pin causes the registers to be updated and this will result in CLKOUT being
disabled. For this reason the first programming sequence should be to enable CLKOUT by setting OSCParam_Clkout to
high for applications using CLKOUT. It is recommended to initialize the XE1205 registers immediately after power-up.
© Semtech 2007
7.5
7.6
CLOCK OUTPUT INTERFACE
DEFAULT SETTINGS AT POWER-UP
OSC_Param_Clkout_freq(1:0)
others
000
001
010
011
Table 27: Frequency divider output
39
CLKOUT frequency
1.22 MHz
2.44 MHz
4.87 MHz
9.75 MHz
19.5 MHz
XE1205
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