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DOC E10523 Rev.D
Interactive Circuits And Systems Ltd. 2000
45
the device specification requires that a zero must be inserted in the word after each
occasion when three one's have been transmitted to the device, regardless of whether the
next bit is a 0 or a 1. This procedure is known as "bit stuffing". For this reason, the actual
length of a programming word may vary between 22 and 29 bits.
For example, to send this programming data:
Last Bit
First Bit
1111 0101
0111
1110
111111
Transmit this serial bit stream:
Last Bit
First Bit
10111 0101
00111
01110
01110111
The fields of the programming word are described in Table 6.2.
Table 6.2
Field
Bits
# of
Bits
Notes
P Counter value (P) <21:15> 7
MSB (Most Significant
Bits)
Duty Cycle Adjust
Up (D)
<14>
1
Set to logic 0
Mux (M)
<13:11> 3
Q Counter Value (Q) <10:4>
7
Index (I)
<3:0>
4
LSB (Least Significant
Bits)
The frequency of the programmable oscillator f
VCO
, and the output frequency f
OUT
are
determined by these fields as follows:
f
VCO
= 2 * f
REF
* (P+3)/(Q+2)
where, f
REF
= Reference frequency (i.e. 14.31818 MHz)
f
OUT
= f
VCO
/ 2
M
Содержание ICS-130
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