C8051F320 Silicon Laboratories Inc, C8051F320 Datasheet - Page 120

• Manufacturer Part Number: C8051F320
• Description: IC 8051 MCU 16K FLASH 32LQFP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F32xr

Specifications of C8051F320

• 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: 25
• 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 17x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

C8051F320/1
13.2. External Oscillator Drive Circuit
The external oscillator circuit may drive an external crystal, ceramic resonator, capacitor, or RC network. A CMOS
clock may also provide a clock input. For a crystal or ceramic resonator configuration, the crystal/resonator must be
wired across the XTAL1 and XTAL2 pins as shown in Option 1 of Figure 13.1. A 10 MΩ resistor also must be wired
across the XTAL1 and XTAL2 pins for the crystal/resonator configuration. In RC, capacitor, or CMOS clock config-
uration, the clock source should be wired to the XTAL2 pin as shown in Option 2, 3, or 4 of Figure 13.1. The type of
external oscillator must be selected in the OSCXCN register, and the frequency control bits (XFCN) must be selected
appropriately (see Figure 13.4)
Important Note on External Oscillator Usage: Port pins must be configured when using the external oscillator cir-
cuit. When the external oscillator drive circuit is enabled in crystal/resonator mode, Port pins P0.2 and P0.3 are used
as XTAL1 and XTAL2 respectively. When the external oscillator drive circuit is enabled in capacitor, RC, or CMOS
clock mode, Port pin P0.3 is used as XTAL2. The Port I/O Crossbar should be configured to skip the Port pins used
by the oscillator circuit; see
Additionally, when using the external oscillator circuit in crystal/resonator, capacitor, or RC mode, the associated
Port pins should be configured as analog inputs. In CMOS clock mode, the associated pin should be configured as a
digital input. See
13.2.1. Clocking Timers Directly Through the External Oscillator
The external oscillator source divided by eight is a clock option for the timers
and the Programmable Counter Array (PCA)
When the external oscillator is used to clock these peripherals, but is not used as the system clock, the external oscil-
lator frequency must be less than or equal to the system clock frequency. In this configuration, the clock supplied to
the peripheral (external oscillator / 8) is synchronized with the system clock; the jitter associated with this synchroni-
zation is limited to ±0.5 system clock cycles.
13.2.2. External Crystal Example
If a crystal or ceramic resonator is used as an external oscillator source for the MCU, the circuit should be configured
as shown in Figure 13.1, Option 1. The External Oscillator Frequency Control value (XFCN) should be chosen from
the Crystal column of the table in Figure 13.4 (OSCXCN register). For example, a 12 MHz crystal requires an XFCN
setting of 111b.
When the crystal oscillator is first enabled, the oscillator amplitude detection circuit requires a settling time to
achieve proper bias. Introducing a delay of 1 ms between enabling the oscillator and checking the XTLVLD bit will
prevent a premature switch to the external oscillator as the system clock. Switching to the external oscillator before
the crystal oscillator has stabilized can result in unpredictable behavior. The recommended procedure is:
Important Note on External Crystals: 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. The traces should be as short as possible and
shielded with ground plane from any other traces which could introduce noise or interference.
120
Step 1. Enable the external oscillator.
Step 2. Wait at least 1 ms.
Step 3. Poll for XTLVLD => ‘1’.
Step 4. Switch the system clock to the external oscillator.
Section “14.2. Port I/O Initialization” on page 131
Section “14.1. Priority Crossbar Decoder” on page 129
(Section “20. Programmable Counter Array (PCA0)” on page
Rev. 1.1
for details on Port input mode selection.
(Section “19. Timers” on page
for Crossbar configuration.
235).
217)