Wiznet W7500, Справочное руководство

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W7500x Reference Manual Version1.1.0
42 / 399
For 𝐶
𝐿𝑜𝑎𝑑1
and 𝐶
𝐿𝑜𝑎𝑑2
, it is recommended to use external ceramic capacitors in the 5 pF to 25
pF range(typ.) and are usually the same size, designed for application, and selected to match
the requirements of the crystal or resonator (see Figure 5).
Refer to the crystal resonator manufacturer for more details on the resonator characteristics
(frequency, package, accuracy).
1
𝑅
𝐸𝑋𝑇
value depends on the crystal characteristics
Figure 5 Typical application with an 8 MHz crystal
RC oscillator clock
RC oscillator clock (RCLK) signal is generated from an internal 8MHz RC oscillator.
RC oscillator has the advantage of providing a clock source at low cost (no external
components). However the RC oscillator is less accurate than the external crystal or ceramic
resonator.
 Accuracy : 1% at T
A
= 25 o C (User don’t need to calibration)
PLL
The internal PLL can be used to multiply the External Oscillator Clock (OCLK) or RC Oscillator
Clock (RCLK). PLL input can be selected by register.
PLL output clock can be generated by following the equations below.

FOUT = FIN x M / N x 1 / OD

Where:

M = M[5] x 2 5 + M[4] x 2 4 + M[3] x 2 3 + M[2] x 2 2 + M[1] x 2 + M[0] x 1

N = N[5] x 2 5 + N[4] x 2 4 + N[3] x 2 3 + N[2] x 2 2 + N[1] x 2 + N[0] x 1

OD = 2 (2 x OD[1]) x 2 (1 x OD[0])
Generated clock
Each generated clock source can be selected among 3 clock source as independent by each
clock source select register.
1 𝑅
𝐸𝑋𝑇
value depends on the crystal characteristics