C8051F540-IQR Silicon Labs, C8051F540-IQR Datasheet - Page 145

• Manufacturer Part Number: C8051F540-IQR
• Description: 8-bit Microcontrollers - MCU 50 MIPS 16 kB 1 kB LIN 2.1 SPI
• Manufacturer: Silicon Labs

Specifications of C8051F540-IQR

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

17.4.2. 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 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, 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 17.6, the required XFCN setting is 010b.
17.4.3. 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 according to Equation 17.2, where f = the frequency of
oscillation in MHz, C = the capacitor value in pF, and V
Figure 17.3. External 32.768 kHz Quartz Crystal Oscillator Connection Diagram
3
)/RC = 1.23(10
22pF*
* Capacitor values depend on
Equation 17.1. RC Mode Oscillator Frequency
3
)/[246 x 50] = 0.1 MHz = 100 kHz
crystal specifications
32.768 kHz
10M
f
=
1.23 10
Rev. 1.1

22pF*
DD
3

= the MCU power supply in Volts.

R C

XTAL1
XTAL2

C8051F54x
145