C8051F350-TB Silicon Laboratories Inc, C8051F350-TB Datasheet - Page 133
C8051F350-TB
Manufacturer Part Number
C8051F350-TB
Description
PROTOTYPINGBOARDWITH C8051F350
Manufacturer
Silicon Laboratories Inc
Type
MCUr
Specifications of C8051F350-TB
Contents
Board
Processor To Be Evaluated
C8051F35x
Interface Type
USB
Silicon Manufacturer
Silicon Labs
Core Architecture
8051
Silicon Core Number
C8051F350
Silicon Family Name
C8051F35x
Kit Contents
Board
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
For Use With/related Products
C8051F350
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
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C8051F350/1/2/3
17.2.3. 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 17.1, 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 kΩ and C = 50 pF:
3
3
f = 1.23( 10
) / RC = 1.23 ( 10
) / [ 246 * 50 ] = 0.1 MHz = 100 kHz
Referring to the table in SFR Definition 17.3, the required XFCN setting is 010b. Programming XFCN to a
higher setting in RC mode will improve frequency accuracy at an increased external oscillator supply cur-
rent.
17.2.4. External Capacitor Example
If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in
Figure 17.1, 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 capaci-
tor to be used and find the frequency of oscillation from the equations below. Assume V
= 3.0 V and
DD
f = 150 kHz:
f = KF / (C x V
)
DD
0.150 MHz = KF / (C x 3.0)
Since the frequency of roughly 150 kHz is desired, select the K Factor from the table in SFR Definition 17.3
as KF = 22:
0.150 MHz = 22 / (C x 3.0)
C x 3.0 = 22 / 0.150 MHz
C = 146.6 / 3.0 pF = 48.8 pF
Therefore, the XFCN value to use in this example is 011b and C = 50 pF.
Rev. 1.1
133
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