C8051F005DK Silicon Laboratories Inc, C8051F005DK Datasheet - Page 102

• Manufacturer Part Number: C8051F005DK
• Description: DEV KIT FOR F005/006/007
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F005DK

• Contents: Evaluation Board, Power Supply, USB Cables, Adapter and Documentation
• Processor To Be Evaluated: C8051F01x
• Interface Type: USB
• Silicon Manufacturer: Silicon Labs
• Core Architecture: 8051
• Silicon Core Number: C8051F005
• Silicon Family Name: C8051F00x
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Silicon Laboratories C8051 F005/006/007
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1188

14.1.
If a crystal or ceramic resonator were used to generate the system clock for the MCU, the circuit would be as shown
in Figure 14.1, Option 1. For an ECS-110.5-20-4 crystal, the resonate frequency is 11.0592MHz, the intrinsic
capacitance is 7pF, and the ESR is 60. The compensation capacitors should be 33pF each, and the PWB parasitic
capacitance is estimated to be 2pF. The appropriate External Oscillator Frequency Control value (XFCN) from the
Crystal column in the table in Figure 14.3 (OSCXCN Register) should be 111b.
Because the oscillator detect circuitry needs time to settle after the crystal oscillator is enabled, software should wait
at least 1ms between enabling the crystal oscillator and polling the XTLVLD bit. The recommend procedure is:
1. Enable the external oscillator
2. Wait at least 1 ms
3. Poll for XTLVLD '0' ==> '1'
4. Switch to the external oscillator
Switching to the external oscillator before the crystal oscillator has stabilized could result in unpredictable behavior.
NOTE: Crystal oscillator circuits are quite sensitive to PCB layout. The crystal should be placed as close as possible
to the XTAL pins on the device, keeping the traces as short as possible and shielded with ground plane from any
other traces which could introduce noise or interference.
14.2.
If an external RC network were used to generate the system clock for the MCU, the circuit would be as shown in
Figure 14.1, Option 2. The capacitor must be no greater than 100pF, but using a very small capacitor will increase
the frequency drift due to the PWB parasitic capacitance. To determine 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 100kHz, let R = 246k and C = 50pF:
14.3.
If an external capacitor were used to generate the system clock for the MCU, the circuit would be as shown in
Figure 14.1, Option 3. The capacitor must be no greater than 100pF, but using a very small capacitor will increase
the frequency inaccuracy due to the PWB parasitic capacitance. To determine the required External Oscillator
Frequency Control value (XFCN) in the OSCXCN Register, select the capacitor to be used and find the frequency
of oscillation from the equations below. Assume AV+ = 3.0V and C = 50pF:
If a frequency of roughly 90kHz is desired, select the K Factor from the table in Figure 14.3 as KF = 13:
Therefore, the XFCN value to use in this example is 011.
f = 1.23(10
XFCN  log
XFCN  log
XFCN  2, or code 010
f = KF / (C * VDD) = KF / (50 * 3)
f = KF / 150
f = 13 /150 = 0.087MHz, or 87kHz
External Crystal Example
External RC Example
External Capacitor Example
3
)/RC = 1.23(10
2
2
(f/25kHz)
(100kHz/25kHz) = log
3
) / [246 * 50] = 0.1MHz = 100kHz
2
(4)
Rev. 1.7
C8051F000/1/2/5/6/7
C8051F010/1/2/5/6/7
102