C8051F321R Silicon Laboratories Inc, C8051F321R Datasheet - Page 121

• Manufacturer Part Number: C8051F321R
• Description: IC 8051 MCU 16K FLASH 28MLP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F32xr

Specifications of C8051F321R

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 25MHz
• Connectivity: SMBus (2-Wire/I²C), SPI, UART/USART, USB
• Peripherals: Brown-out Detect/Reset, POR, PWM, Temp Sensor, WDT
• Number Of I /o: 21
• Program Memory Size: 16KB (16K x 8)
• Program Memory Type: FLASH
• Ram Size: 2.25K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Data Converters: A/D 13x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-VQFN Exposed Pad, 28-HVQFN, 28-SQFN, 28-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Other names: 336-1067-2

C8051F320/1
13.2.3. 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 13.1, 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 determine the required External Oscil-
lator 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 Figure 13.4, 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 current.
13.2.4. External Capacitor Example
If a capacitor is used as an external oscillator for the MCU, the circuit should be configured as shown in Figure 13.1,
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 Fre-
quency Control value (XFCN) in the OSCXCN Register, select the capacitor to be used and find the frequency of
oscillation from the equations below. Assume VDD = 3.0 V and C = 50 pF:
f = KF / ( C * VDD ) = KF / ( 50 * 3 ) MHz
f = KF / 150 MHz
If a frequency of roughly 150 kHz is desired, select the K Factor from the table in Figure 13.4 as KF = 22:
f = 22 / 150 = 0.146 MHz, or 146 kHz
Therefore, the XFCN value to use in this example is 011b.
Rev. 1.1
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