C8051F962-A-GM Silicon Labs, C8051F962-A-GM Datasheet - Page 300

• Manufacturer Part Number: C8051F962-A-GM
• Description: 8-bit Microcontrollers - MCU 128KB, DC-DC, AES DQFN76
• Manufacturer: Silicon Labs

Specifications of C8051F962-A-GM

• Rohs: yes
• Core: 8051
• Processor Series: C8051
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 25 MHz
• Program Memory Size: 128 KB
• Data Ram Size: 8448 B
• On-chip Adc: Yes
• Operating Supply Voltage: 2.5 V to 3.3 V
• Operating Temperature Range: - 40 C to + 85 C
• Package / Case: DQFN-76
• Mounting Style: SMD/SMT
• Number Of Programmable I/os: 57
• Number Of Timers: 4

C8051F96x
24.2. SmaRTClock Clocking Sources
The SmaRTClock peripheral is clocked from its own timebase, independent of the system clock. The
SmaRTClock timebase can be derived from an external CMOS clock, the internal LFO, or the SmaRT-
Clock oscillator circuit, which has two modes of operation: Crystal Mode, and Self-Oscillate Mode. The
oscillation frequency is 32.768 kHz in Crystal Mode and can be programmed in the range of 10 kHz to
40 kHz in Self-Oscillate Mode. The internal LFO frequency is 16.4 kHz ±20%. The frequency of the
SmaRTClock oscillator can be measured with respect to another oscillator using an on-chip timer. See
Section “32. Timers” on page 444 for more information on how this can be accomplished.
Note: The SmaRTClock timebase can be selected as the system clock and routed to a port pin. See Section
24.2.1. Using the SmaRTClock Oscillator with a Crystal or External CMOS Clock
When using Crystal Mode, a 32.768 kHz crystal should be connected between XTAL3 and XTAL4. No
other external components are required. The following steps show how to start the SmaRTClock crystal
oscillator in software:
In Crystal Mode, the SmaRTClock oscillator may be driven by an external CMOS clock. The CMOS clock
should be applied to XTAL3. XTAL34 should be left floating. In this mode, the external CMOS clock is ac
coupled into the SmaRTClock and should have a minimum voltage swing of 400 mV. The CMOS clock sig-
nal voltage should not exceed VDD or drop below GND. Bias levels closer to VDD will result in lower I/O
power consumption because the XTAL3 pin has a built-in weak pull-up. The SmaRTClock oscillator should
be configured to its lowest bias setting with AGC disabled. The CLKVLD bit is indeterminate when using a
CMOS clock, however, the OSCFAIL bit may be checked 2 ms after SmaRTClock oscillator is powered on
to ensure that there is a valid clock on XTAL3. The CLKVLD bit is forced low when BIASX2 is disabled.
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1. Configure the XTAL3 and XTAL4 pins for Analog I/O.
2. Set SmaRTClock to Crystal Mode (XMODE = 1).
3. Disable Automatic Gain Control (AGCEN) and enable Bias Doubling (BIASX2) for fast crystal startup.
4. Set the desired loading capacitance (RTC0XCF).
5. Enable power to the SmaRTClock oscillator circuit (RTC0EN = 1).
6. Wait 20 ms.
7. Poll the SmaRTClock Clock Valid Bit (CLKVLD) until the crystal oscillator stabilizes.
8. Poll the SmaRTClock Load Capacitance Ready Bit (LOADRDY) until the load capacitance reaches
9. Enable Automatic Gain Control (AGCEN) and disable Bias Doubling (BIASX2) for maximum power
10. Enable the SmaRTClock missing clock detector.
11. Wait 2 ms.
12. Clear the PMU0CF wake-up source flags.
its programmed value.
savings.
“23. Clocking Sources” on page 286 for information on selecting the system clock source and Section “27. Port
Input/Output” on page 351 for information on how to route the system clock to a port pin. The SmaRTClock
timebase can also be routed to a port pin while the device is in its ultra low power sleep mode. See the
PMU0MD register description for details.
Rev. 0.5