C8051T630DK Silicon Laboratories Inc, C8051T630DK Datasheet - Page 108

• Manufacturer Part Number: C8051T630DK
• Description: KIT DEV FOR C8051T630 FAMILY
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051T630DK

• Contents: Board, daughter boards, power adapter, cables, documentation and software
• Processor To Be Evaluated: C8051T63x
• Interface Type: USB
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: C8051T630, T631, T632, T633, T634 and T635 MCUs
• For Use With: 336-1465 - BOARD SOCKET DAUGHTER 20-QFN
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1464

C8051T630/1/2/3/4/5
19.4.1. 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, “RC Mode”. 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, according to Equation 19.1,
where f = the frequency of oscillation in MHz, C = the capacitor value in pF, and R = the pull-up resistor
value in k.
For example: If the frequency desired is 100 kHz, let R = 246 k and C = 50 pF:
f = 1.23( 10
Referring to the table in SFR Definition 19.5, the required XFCN setting is 010b.
19.4.2. 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, “C Mode”. 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 according to Equation 19.2, where f = the frequency of
oscillation in MHz, C = the capacitor value in pF, and V
For example: Assume V
f = KF / (C x VDD)
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 19.5
(OSCXCN) 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.
108
3
) / RC = 1.23 ( 10
Equation 19.1. RC Mode Oscillator Frequency
DD
Equation 19.2. C Mode Oscillator Frequency
= 3.0 V and f = 150 kHz:
3
) / [ 246 x 50 ] = 0.1 MHz = 100 kHz
f
f
=
=
1.23 10

KF
Rev. 1.0




R V
3
DD



R C
= the MCU power supply in Volts.
DD


