C8051F411EK Silicon Laboratories Inc, C8051F411EK Datasheet - Page 170

• Manufacturer Part Number: C8051F411EK
• Description: KIT EVAL FOR C8051F411
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F411EK

• Contents: Evaluation Board, CD-ROM, USB Cable, Batteries and User Guide
• Processor To Be Evaluated: C8051F41x
• Interface Type: USB
• Silicon Manufacturer: Silicon Labs
• Core Architecture: 8051
• Silicon Core Number: C8051F411
• Silicon Family Name: C8051F41x
• Kit Contents: LCD Based Evaluation Board, USB Cable, Software CD And Quick-Start Guide
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Silicon Laboratories C8051F41x
• For Use With: 336-1315 - KIT REF DESIGN VOICE RECORD F41X
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1317

C8051F410/1/2/3
19.2.3. 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 19.1, 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 19.3, 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.
19.2.4. External Capacitor Example
If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in
Figure 19.1, 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
= 2.0 V and f = 75 kHz:
DD
f = KF / (C x V
)
DD
0.075 MHz = KF / (C x 2.0)
Since the frequency of roughly 75 kHz is desired, select the K Factor from the table in SFR Definition 19.3
as KF = 7.7:
0.075 MHz = 7.7 / (C x 2.0)
C x 2.0 = 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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