C8051F351 Silicon Laboratories Inc, C8051F351 Datasheet - Page 131

• Manufacturer Part Number: C8051F351
• Description: IC 8051 MCU 8K FLASH 28MLP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F35xr

Specifications of C8051F351

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 50MHz
• Connectivity: SMBus (2-Wire/I²C), SPI, UART/USART
• Peripherals: POR, PWM, Temp Sensor, WDT
• Number Of I /o: 17
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 768 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Data Converters: A/D 8x24b; D/A 2x8b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-VQFN Exposed Pad, 28-HVQFN, 28-SQFN, 28-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -

17.4. 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 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[1:0] bits in register CLKSEL select which oscillator source is used as the system clock.
CLKSL[1:0] must be set to 01b for the system clock to run from the external oscillator; however the exter-
nal oscillator may still clock certain peripherals (timers, PCA) when the internal oscillator is selected as the
system clock. The system clock may be switched on-the-fly between the internal oscillator, external oscilla-
tor, and Clock Multiplier so long as the selected clock source is enabled and has settled.
-40 to +85 °C unless otherwise specified
Internal Oscillator Frequency
Internal Oscillator Supply
Current (from V
†
Applies only to external oscillator sources.
Bits7-2:
Bits1-0:
Bit7
R
-
Parameter
Unused. Read = 000000b; Write = don’t care.
CLKSL1-0: System Clock Select
These bits select the system clock source.
DD
Bit6
R
-
)
CLKSL
Table 17.1. Oscillator Electrical Characteristics
00
01
10
11
Figure 17.6. CLKSEL: Clock Select Register
Bit5
R
-
Reset Frequency
OSCICN.7 = 1
Bit4
R
Internal Oscillator (as determined by the
-
Conditions
IFCN bits in register OSCICN)
Rev. 0.4
Bit3
External Oscillator
R
-
Selected Clock
Clock Multiplier
RESERVED
Bit2
R
-
Min
C8051F350/1/2/3
24
R/W
Bit1
CLKSL
TBD
24.5
Typ
SFR Address:
R/W
Bit0
Max
25
0xA9
00000000
Reset Value
Units
MHz
µA
131