C8051F709-GQR Silicon Labs, C8051F709-GQR Datasheet - Page 178

• Manufacturer Part Number: C8051F709-GQR
• Description: 8-bit Microcontrollers - MCU 8kB 32B EEPROM Cap Sense
• Manufacturer: Silicon Labs

Specifications of C8051F709-GQR

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit

C8051F70x/71x
27.3.2. 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 27.1, 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, according to Equation , 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 27.4, the required XFCN setting is 010b.
178
Figure 27.2. External 32.768 kHz Quartz Crystal Oscillator Connection Diagram
3
) / RC = 1.23 ( 10
22pF*
* Capacitor values depend on
Equation 27.1. RC Mode Oscillator Frequency
crystal specifications
3
) / [ 246 x 50 ] = 0.1 MHz = 100 kHz
32.768 kHz
10M
f
=
1.23 10
Rev. 1.0

22pF*
3


R C

XTAL1
XTAL2
