C8051F961-A-GM Silicon Labs, C8051F961-A-GM Datasheet - Page 289

• Manufacturer Part Number: C8051F961-A-GM
• Description: 8-bit Microcontrollers - MCU 128KB, DC-DC, LCD AES, QFN40
• Manufacturer: Silicon Labs

Specifications of C8051F961-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: QFN-40
• Mounting Style: SMD/SMT
• Number Of Programmable I/os: 34
• Number Of Timers: 4

23.3.2. External RC Mode
If an RC network is used as the external oscillator, the circuit should be configured as shown in
Figure 23.1, Option 2. The RC network should be added to XTAL2, and XTAL2 should be configured for
analog I/O with the digital output drivers disabled. XTAL1 is not affected in RC mode.
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. The resistor should be no smaller than
10 k. The oscillation frequency can be determined by the following equation:
where
f = frequency of clock in MHzR = pull-up resistor value in k
V
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. For example, if the fre-
quency desired is 100 kHz, let R = 246 k and C = 50 pF:
where
f = frequency of clock in MHz
V
Referencing Table 23.2, the recommended XFCN setting is 010.
When the RC oscillator is first enabled, the external oscillator valid detector allows software to determine
when oscillation has stabilized. The recommended procedure for starting the RC oscillator is as follows:
DD
DD
1. Configure XTAL2 for analog I/O and disable the digital output drivers.
2. Configure and enable the external oscillator.
3. Poll for XTLVLD > 1.
4. Switch the system clock to the external oscillator.
f
= power supply voltage in VoltsC = capacitor value on the XTAL2 pin in pF
= power supply voltage in Volts
f
=
XFCN
=
000
001
010
100
101
011
110
111
1.23 10
------------------------ -
1.23 10
------------------------ -
R C
R




C
3
Table 23.2. Recommended XFCN Settings for RC and C modes
3
=
Frequency Range (RC
800 kHz f 1.6 MHz
1.6 MHz f 3.2 MHz
100 kHz f 200 kHz
200 kHz f 400 kHz
400 kHz f 800 kHz
50 kHz f 100 kHz
1.23 10
------------------------ -
25 kHz f 50 kHz
246 50
and C Mode)
Approximate


f 25 kHz
3
=
100 kHz
R = pull-up resistor value in k
C = capacitor value on the XTAL2 pin in pF
K Factor (C Mode)
Rev. 0.5
K Factor = 1590
K Factor = 0.87
K Factor = 180
K Factor = 664
K Factor = 2.6
K Factor = 7.7
K Factor = 22
K Factor = 65
Typical Supply Current/ Actual
242 µA, f = 890 kHz, C = 46 pF
1.0 mA, f = 2.0 MHz, C = 46 pF
4.6 mA, f = 6.8 MHz, C = 46 pF
32 µA, f = 270 kHz, C = 33 pF
82 µA, f = 310 kHz, C = 46 pF
5.5 µA, f = 33 kHz, C = 33 pF
3.0 µA, f = 11 kHz, C = 33 pF
13 µA, f = 98 kHz, C = 33 pF
(C Mode, VDD = 2.4 V)
Measured Frequency
C8051F96x
289