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MC12429 データシート(PDF) 4 Page - Motorola, Inc |
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MC12429 データシート(HTML) 4 Page - Motorola, Inc |
4 / 12 page MC12429 MOTOROLA TIMING SOLUTIONS 4 9–BIT SR 2–BIT SR 3–BIT SR DIV 16 Figure 3. MC12429 Block Diagram (28–Lead PLCC Pinout) 16MHz S_LOAD P_LOAD S_DATA S_CLOCK XTAL1 XTAL2 OSC 4 5 PHASE DETECTOR 28 7 9–BIT DIV M COUNTER LATCH VCO DIV N (1, 2, 4, 8) LATCH 200–400 MHz FOUT FOUT +3.3 or 5.0V 25 24 23 VCC0 LATCH TEST 20 +3.3 or 5.0V PLL_VCC 1MHz FREF 01 27 26 01 VCC1 +3.3 or 5.0V M[8:0] 9 8 16 N[1:0] 2 17, 18 21 22, 19 OE 6 PROGRAMMING INTERFACE Programming the device amounts to properly configuring the internal dividers to produce the desired frequency at the outputs. The output frequency can by represented by this formula: FOUT = (FXTAL ÷ 16) x M ÷ N (1) Where FXTAL is the crystal frequency, M is the loop divider modulus, and N is the output divider modulus. Note that it is possible to select values of M such that the PLL is unable to achieve loop lock. To avoid this, always make sure that M is selected to be 200 ≤ M ≤ 400 for a 16MHz input reference. Assuming that a 16MHz reference frequency is used the above equation reduces to: FOUT = M ÷ N Substituting the four values for N (1, 2, 4, 8) yields: TABLE A: Output Frequency Range N FOUT OUTPUT FREQUENCY RANGE 1 2 4 8 M M / 2 M / 4 M / 8 200 – 400 MHZ 100 – 200 MHZ 50 – 100 MHZ 25 – 50 MHZ From these ranges the user will establish the value of N required, then the value of M can be calculated based on the appropriate equation above. For example if an output frequency of 131MHz was desired the following steps would be taken to identify the appropriate M and N values. 131MHz falls within the frequency range set by an N value of 2 so N [1:0] = 01. For N = 2 FOUT = M ÷ 2 and M = 2 x FOUT. Therefore M = 131 x 2 = 262, so M[8:0] = 100000110. Following this same procedure a user can generate any whole frequency desired between 25 and 400MHz. Note that for N > 2 fractional values of FOUT can be realized. The size of the programmable frequency steps (and thus the indicator of the fractional output frequencies acheivable) will be equal to FXTAL ÷ 16 ÷ N. For input reference frequencies other than 16MHz the set of appropriate equations can be deduced from equation 1. For computer applications another useful frequency base would be 16.666MHz. From this reference one can generate a family of output frequencies at multiples of the 33.333MHz PCI clock. As an example to generate a 133.333MHz clock from a 16.666MHz reference the following M and N values would be used: FOUT = 16.666 ÷ 16 x M ÷ N = 1.0416 x M ÷ N |
同様の部品番号 - MC12429 |
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同様の説明 - MC12429 |
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