XE1203 ETC1 [List of Unclassifed Manufacturers], XE1203 Datasheet - Page 32

• Manufacturer Part Number: XE1203
• Description: Low-Power, integrated UHF transceiver
• Manufacturer: ETC1 [List of Unclassifed Manufacturers]

5.4
The reference clock used for the frequency synthesizer and internal digital circuit can be generated internally using
internal amplifier and external quartz crystal or provided by an external oscillator. In the case of external oscillator,
the register “RTParam_Osc” has to be set high, and the external clock signal at 39 MHz has to be applied to the
pin “XTA”.
The chip can be used with a 39 MHz quartz crystal running on its fundamental frequency or with 3
frequency. The third overtone operation requires a resistor in parallel to the quartz. This resistor can be selected by
programming the register ADParam_Resxosc(3:0). The required value depends on the crystal used.
ADParam_Resxosc(3:0) is set to ”0000’’ by default, which imposes a resistor of 3.8 MOhms in parallel to the
crystal. This default value is used with a 39 MHz crystal running on its fundamental frequency. In the case of
overtone operation of the quartz crystal, where the microcontroller uses the XE1203 as a clock source, user should
be aware that during power up the XE1203 oscillator starts at fundamental frequency and after programming the
oscillator switch to overtone operation. Therefore, a wait can be required for the oscillator to settle down before
doing time sensitive operations.
5.5
When RTParam_Clkout is set high, a frequency divider by 4, 8, 16, 32, depending on ADParam_Clkfreq is
embedded in the chip and provides the CLKOUT clock signal for an MCU or an external circuitry. The input
frequency of this divider is the 39.0 MHz reference frequency, so the possible output frequencies are listed in the
next table.
When the XE1203 is in sleep mode, then this clock is stopped even if RTParam_Clkout remains high.
5.6
The internally generated power on reset signal sets the RTParam, FSParam, ADParam and Pattern registers to
00hex. Only exception is CLKOUT generation, although RTPAram_CLkout is set to low, i.e disabled, the XE1203
generates a CLKOUT signal in order to let the microcontroller operate.
The first rising edge on EN pin causes the registers to be updated and this will result CLKOUT to be disabled. For
this reason the first programming sequence should be enabling CLKOUT by setting RTPAram_CLkout register to
high for applications using CLKOUT. Initializing the XE1203 registers immediately after power-up according to the
application needs is strongly recommended.
32
SELECTION OF THE REFERENCE FREQUENCY
CLOCK OUTPUT INTERFACE
DEFAULT SETTINGS AT POWER-UP
ADParam_Clkfreq
00
01
10
11
CLKOUT frequency
1.22 MHz
2.44 MHz
4.87 MHz
9.75 MHz
Data Sheet
XE1203
D0308-214
rd
overtone