C8051F521-IMR Silicon Labs, C8051F521-IMR Datasheet - Page 143

• Manufacturer Part Number: C8051F521-IMR
• Description: 8-bit Microcontrollers - MCU 8KB 12ADC 125C 10Pin MCU
• Manufacturer: Silicon Labs

Specifications of C8051F521-IMR

• Product Category: 8-bit Microcontrollers - MCU
• Rohs: yes
• Core: 8051
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 25 MHz
• Program Memory Size: 8 KB
• Data Ram Size: 256 B
• On-chip Adc: Yes
• Package / Case: DFN-10
• Mounting Style: SMD/SMT
• A/d Bit Size: 12 bit
• A/d Channels Available: 6
• Interface Type: SPI, UART
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 6
• Number Of Timers: 3
• On-chip Dac: No
• Processor Series: C8051
• Program Memory Type: Flash
• Factory Pack Quantity: 1500
• Supply Voltage - Max: 2.7 V, 5.25 V
• Supply Voltage - Min: 2 V, 2.7 V

14.3. System Clock Selection
The internal oscillator requires little start-up time and may be selected as the system clock immediately fol-
lowing the OSCICN write that enables the internal oscillator. External crystals and ceramic resonators typ-
ically require a start-up time before they are settled and ready for use. The Crystal Valid Flag (XTLVLD in
register OSCXCN) is set to 1 by hardware when the external oscillator is settled. To avoid reading a false
XTLVLD in crystal mode, the software should delay at least 1 ms between enabling the external
oscillator and checking XTLVLD. RC and C modes typically require no startup time.
The CLKSL bit in register CLKSEL selects which oscillator source is used as the system clock. CLKSL
must be set to 1 for the system clock to run from the external oscillator; however the external oscillator may
still clock certain peripherals (timers, PCA) when another oscillator is selected as the system clock. The
system clock may be switched on-the-fly between the internal oscillator and external oscillator, as long as
the selected clock source is enabled and has settled.
SFR Definition 14.5. CLKSEL: Clock Select
Bits7–6: Unused. Read = 00b; Write = don’t care.
Bits5–4: Reserved. Read = 00b; Must write 00b.
Bit3:
Bits2–1: Reserved. Read = 00b; Must write 00b.
Bit0:
Bit7
R
-
Unused. Read = 0b; Write = don’t care.
CLKSL: System Clock Select
0: Internal Oscillator (as determined by the IFCN bits in register OSCICN).
1: External Oscillator.
Bit6
R
-
Reserved Reserved
R/W
Bit5
R/W
Bit4
Rev. 1.4
Bit3
R
-
Reserved Reserved
R/W
Bit2
C8051F52x/F53x
R/W
Bit1
SFR Address:
CLKSL
R/W
Bit0
00000000
Reset Value
0xA9
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