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Philips Semiconductors
Volume 1
3.7.10 Procedure for detrmining PLL settings
If a particular application uses the PLL, its configuration may be determined as follows:
Table 20:
PSEL Bits (PLLCFG bits [6:5])
00
01
10
11
Table 21:
MSEL Bits (PLLCFG bits [4:0])
00000
00001
00010
00011
...
11110
11111
3.7.11 PLL example
System design asks for F
Based on these specifications, M = CCLK / Fosc = 60 MHz / 10 MHz = 6. Consequently,
M - 1 = 5 will be written as PLLCFG[4:0].
Value for P can be derived from P = F
in range of 156 MHz to 320 MHz. Assuming the lowest allowed frequency for
F
produces P = 2.67. The only solution for P that satisfies both of these requirements and is
listed in
User manual
1. Choose the desired processor operating frequency (CCLK). This may be based on
processor throughput requirements, need to support a specific set of UART baud
rates, etc. Bear in mind that peripheral devices may be running from a lower clock
than the processor (see
2. Choose an oscillator frequency (F
multiple of F
.
OSC
3. Calculate the value of M to configure the MSEL bits. M = CCLK / F
the range of 1 to 32. The value written to the MSEL bits in PLLCFG is M − 1 (see
Table
21.
4. Find a value for P to configure the PSEL bits, such that F
frequency limits. F
CCO
of the values 1, 2, 4, or 8. The value written to the PSEL bits in PLLCFG is 00 for
P = 1; 01 for P = 2; 10 for P = 4; 11 for P = 8 (see
PLL Divider values
PLL Multiplier values
= 156 MHz, P = 156 MHz / (2 x 60 MHz) = 1.3. The highest F
CCO
Table 20
is P = 2. Therefore, PLLCFG[6:5] = 1 will be used.
Rev. 01 — 24 June 2005
Section 3.10 "VPB divider" on page
). CCLK must be the whole (non-fractional)
OSC
is calculated using the equation given above. P must have one
Value of P
1
2
4
8
Value of M
1
2
3
4
...
31
32
= 10 MHz and requires CCLK = 60 MHz.
OSC
/ (CCLK x 2), using condition that F
CCO
UM10120
Chapter 3: System Control Block
38).
. M must be in
OSC
is within its defined
CCO
Table
20).
CCO
frequency criteria
CCO
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
must be
32
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