C8051F530-TB Silicon Laboratories Inc, C8051F530-TB Datasheet - Page 140

• Manufacturer Part Number: C8051F530-TB
• Description: BOARD PROTOTYPE W/C8051F530
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F530-TB

• Contents: Board
• Processor To Be Evaluated: C8051F52xA and C8051F53xA
• Interface Type: USB
• Lead Free Status / RoHS Status: Vendor undefined / Vendor undefined
• For Use With/related Products: C8051F530
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

C8051F52x/F52xA/F53x/F53xA
14.2.3. External RC Example
If an RC network is used as an external oscillator source for the MCU, the circuit should be configured as
shown in Figure 14.1, Option 2. The capacitor should be no greater than 100 pF; however for very small
capacitors, the total capacitance may be dominated by parasitic capacitance in the PCB layout. To deter-
mine the required External Oscillator Frequency Control value (XFCN) in the OSCXCN Register, first
select the RC network value to produce the desired frequency of oscillation. If the frequency desired is
100 kHz, let R = 246 k and C = 50 pF:
3
3
f = 1.23( 10
) / RC = 1.23 ( 10
) / [ 246 x 50 ] = 0.1 MHz = 100 kHz
Referring to the table in SFR Definition 14.4, the required XFCN setting is 010b. Programming XFCN to a
higher setting in RC mode will improve frequency accuracy at a slightly increased external oscillator supply
current.
14.2.4. External Capacitor Example
If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in
Figure 14.1, Option 3. The capacitor should be no greater than 100 pF; however for very small capacitors,
the total capacitance may be dominated by parasitic capacitance in the PCB layout. To determine the
required External Oscillator Frequency Control value (XFCN) in the OSCXCN Register, select the fre-
quency of oscillation and calculate the capacitance to be used from the equations below. Assume
V
= 2.1 V and f = 75 kHz:
DD
f = KF / (C x V
)
DD
0.075 MHz = KF / (C x 2.1)
Since the frequency of roughly 75 kHz is desired, select the K Factor from the table in SFR Definition 14.4
as KF = 7.7:
0.075 MHz = 7.7 / (C x 2.1)
C x 2.1 = 7.7 / 0.075 MHz
C = 102.6 / 2.0 pF = 51.3 pF
Therefore, the XFCN value to use in this example is 010b.
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Rev. 1.3