DOC E10523 Rev.D
Interactive Circuits And Systems Ltd. 2000
48
programming the oscillator to an initial or new frequency is as follows:
1. Load Control register to enable loading of the Programming word register, enable
the output and select the reference frequency for output from the Internal
Multiplexer. The Protocol word follows the control word. All data is shifted in LSB
(Least Significant Bit) first.
Last Bit First Bit
Control word
0 1 1 1 1 0 0 0 0 0 0 1 0 1
Protocol Word Control Reg. Data
2. Shift in the desired output frequency value via a programming word that is 22 bits in
length, plus any required bit stuffs. (Up to 29 bits can be obtained with bit-stuffing).
The example programming word for 12.8 MHz, calculated in section 6.2.6 above, is
shown below.
Last Bit First Bit
Programming word for
12.8 MHz (0x382370)
0 0 1 1 1 0 0 0 0 0 1 0 0 0 1 1 0 1 1 1 0 0 0 0
3. Load the Control register to disable further loading of the Programming word
register. This causes the required output frequency value to be programmed while
keeping the output set to the reference frequency for the time being.
Last Bit First Bit
Control word
0 1 1 1 1 0 0 0 0 0 0 1 0 0
Protocol Word Control Reg. Data
4. Wait at least 10ms for the VCO to settle to the new frequency. The value will be
accurate to within 0.1% within this time.
5. Load the Control register to disable the Internal Multiplexer. This will cause the
output to immediately swing to the new frequency.
Last Bit First Bit
Control word
0 1 1 1 1 0 0 0 0 0 0 0 0 0
Protocol Word Control Reg. Data