C8051F045R Silicon Labs, C8051F045R Datasheet - Page 178

• Manufacturer Part Number: C8051F045R
• Description: 8-bit Microcontrollers - MCU 25 MIPS 64KB 10ADC
• Manufacturer: Silicon Labs

Specifications of C8051F045R

• Product Category: 8-bit Microcontrollers - MCU
• Core: 8051
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 25 MHz
• Program Memory Size: 64 KB
• Data Ram Size: 4.25 KB
• On-chip Adc: Yes
• Operating Supply Voltage: 2.7 V to 3.6 V
• Package / Case: TQFP-64
• Mounting Style: SMD/SMT
• A/d Bit Size: 10 bit
• A/d Channels Available: 13
• Data Rom Size: 64 KB
• Interface Type: CAN, SMBus, SPI, UART
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 32
• Number Of Timers: 16 bit
• Processor Series: C8051
• Program Memory Type: Flash
• Factory Pack Quantity: 500
• Supply Voltage - Max: 3.6 V
• Supply Voltage - Min: 2.7 V

C8051F040/1/2/3/4/5/6/7
14.5. 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 14.1, 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 14.4, the required XFCN setting is 010b.
14.6. External Capacitor Example
If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in
Figure 14.1, 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 desired
frequency of oscillation and find the capacitor to be used from the equations below. Assume V
= 3.0 V
DD
and f = 50 kHz:
f = KF / ( C x V
) = KF / ( C x 3 ) = 0.050 MHz
DD
If a frequency of roughly 50 kHz is desired, select the K Factor from the table in SFR Definition 14.4 as
KF = 7.7:
0.050 MHz = 7.7 / (C x 3)
C x 3 = 7.7 / 0.050 = 154, so C = 154 / 3 pF = 51.3 pF
Therefore, the XFCN value to use in this example is 010b.
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