.hide-partial { max-height: none; } .show-more { display: none; }

Silicon Labs Embedded Processors & Controllers

.catnav-wrapper { height: auto; overflow: visible; } .catalog-nav-tabs ul { white-space: normal; }

Types of Embedded Processors & Controllers

List Images

Results: 2,638

Applied Filters:

Brand = Silicon Labs

Product Type

Mounting Style

Package/Case

Core

Data Bus Width

Maximum Clock Frequency

Program Memory Size

Data RAM Size

ADC Resolution

Number of I/Os

Minimum Operating Temperature

Maximum Operating Temperature

Qualification

Packaging

Reset All

Search within results

In Stock

Normally Stocked

Active

New Products

RoHS Compliant

.search-refine-wrapper { display: inline-block; min-width: 100%; } .scroll-body { overflow-x: visible; } .search-table-wrapper { overflow: visible; } .hide-partial { max-height: none; } .show-more { display: none; }

Part #

ARM Microcontrollers - MCU ARM Cortex-M0+ 32-bit 25 MHz 64 kB MCU

EFM32HG108F64G-C-QFN24
Silicon Labs
1: ₹467.17
4,818In Stock

Mfr. Part No.
EFM32HG108F64G-C-QFN24

Mouser Part No
634-HG108F64GCQFN24

Silicon Labs

ARM Microcontrollers - MCU ARM Cortex-M0+ 32-bit 25 MHz 64 kB MCU

Learn More

Datasheet

4,818In Stock

₹467.17

₹315.34

₹293.78

₹258.74

View

Min.: 1
Mult.: 1

ARM Microcontrollers - MCU

SMD/SMT

QFN-24

ARM Cortex M0+

32 bit

25 MHz

64 kB

8 kB

12 bit

17 I/O

- 40 C

+ 85 C

Tray

RF System on a Chip - SoC Mighty Gecko SoC QFN48 2.4 G 19 dB mesh multi-protocol 1024 kB 256 kB (RAM) 31GPIO

EFR32MG12P432F1024GM48-CR
Silicon Labs
1: ₹1,095.15
2,500In Stock

Mfr. Part No.
EFR32MG12P432F1024GM48-CR

Mouser Part No
634-MG12P432GM48-CR

Silicon Labs

RF System on a Chip - SoC Mighty Gecko SoC QFN48 2.4 G 19 dB mesh multi-protocol 1024 kB 256 kB (RAM) 31GPIO

Learn More

Datasheet

2,500In Stock

Cut Tape

₹1,095.15

₹950.51

₹901.10

₹825.63

View

Reel

₹676.50

Min.: 1
Mult.: 1

Reel: 2,500

RF System on a Chip - SoC

SMD/SMT

QFN-48

ARM Cortex M4

32 bit

40 MHz

1 MB

256 kB

12 bit

31 I/O

- 40 C

+ 85 C

Reel, Cut Tape

RF System on a Chip - SoC Mighty Gecko SoC QFN48 2.4 G 19 dB mesh multi-protocol 512 kB 64 kB (RAM) 31GPIO

EFR32MG13P732F512GM48-DR
Silicon Labs
1: ₹639.66
47,180In Stock

Mfr. Part No.
EFR32MG13P732F512GM48-DR

Mouser Part No
634-MGP732F512GM48DR

Silicon Labs

RF System on a Chip - SoC Mighty Gecko SoC QFN48 2.4 G 19 dB mesh multi-protocol 512 kB 64 kB (RAM) 31GPIO

Learn More

Datasheet

47,180In Stock

Cut Tape

₹639.66

₹589.35

₹570.48

₹545.33

View

Reel

₹456.39

Min.: 1
Mult.: 1

Reel: 2,500

RF System on a Chip - SoC

SMD/SMT

QFN-48

ARM Cortex M4

32 bit

40 MHz

512 kB

64 kbit

12 bit

31 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 32 kB flash 2.304 kB RAM 16 GPIO BB5 8-bit MCU

EFM8BB52F32G-C-QFN20
Silicon Labs
1: ₹142.85
3,614In Stock

Mfr. Part No.
EFM8BB52F32G-C-QFN20

Mouser Part No
634-EFM852F32GCQFN20

Silicon Labs

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 32 kB flash 2.304 kB RAM 16 GPIO BB5 8-bit MCU

Learn More

Datasheet

3,614In Stock

₹142.85

₹100.62

₹87.32

₹82.74

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

16 kB

1.28 kB

16 I/O

- 40 C

+ 85 C

Cut Tape

RF System on a Chip - SoC Mighty Gecko SoC, 2.4 GHz, 256 kB flash, 32 kB RAM, 16.5 dBm, QFN-48, mesh

EFR32MG1B132F256GM48-C0R
Silicon Labs
1: ₹820.24
10,000In Stock
NRND

Mfr. Part No.
EFR32MG1B132F256GM48-C0R

Mouser Part No
634-32MGB132F25648CR

NRND

Silicon Labs

RF System on a Chip - SoC Mighty Gecko SoC, 2.4 GHz, 256 kB flash, 32 kB RAM, 16.5 dBm, QFN-48, mesh

Learn More

Datasheet

10,000In Stock

Cut Tape

₹820.24

₹711.53

₹673.80

₹622.59

View

Reel

₹452.79

MouseReel Available

Min.: 1
Mult.: 1

Reel: 2,500

RF System on a Chip - SoC

SMD/SMT

QFN-48

ARM Cortex M4

32 bit

40 MHz

256 kB

32 kB

12 bit

31 I/O

- 40 C

+ 85 C

Reel, Cut Tape, MouseReel

8-bit Microcontrollers - MCU 8051 25 MHz 32 kB 8-bit MCU

C8051F005-GQR
Silicon Labs
1: ₹2,825.47
576In Stock
NRND

Mfr. Part No.
C8051F005-GQR

Mouser Part No
634-C8051F005-GQR

NRND

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 32 kB 8-bit MCU

Datasheet

576In Stock

Cut Tape

₹2,825.47

₹2,635.01

₹2,634.11

₹2,633.21

View

Reel

₹1,943.24

Min.: 1
Mult.: 1

Reel: 500

8-bit Microcontrollers - MCU

SMD/SMT

TQFP-64

8051

8 bit

25 MHz

32 kB

2.25 kB

12 bit

32 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB 8-bit MCU

C8051F413-GM
Silicon Labs
1: ₹990.94
6,215In Stock
NRND

Mfr. Part No.
C8051F413-GM

Mouser Part No
634-C8051F413-GM

NRND

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB 8-bit MCU

Datasheet

6,215In Stock

₹990.94

₹826.53

₹812.15

₹729.50

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-28

8051

8 bit

50 MHz

16 kB

2.31 kB

12 bit

20 I/O

- 40 C

+ 85 C

Tube

RF System on a Chip - SoC Mighty Gecko SoC, 2.4 GHz, 256 kB flash, 32 kB RAM, 19.5 dBm, QFN-32, mesh

EFR32MG1B232F256GM32-C0R
Silicon Labs
1: ₹835.51
7,500In Stock
NRND

Mfr. Part No.
EFR32MG1B232F256GM32-C0R

Mouser Part No
634-32MGB232F25632CR

NRND

Silicon Labs

RF System on a Chip - SoC Mighty Gecko SoC, 2.4 GHz, 256 kB flash, 32 kB RAM, 19.5 dBm, QFN-32, mesh

Learn More

Datasheet

7,500In Stock

Cut Tape

₹835.51

₹725.01

₹686.38

₹633.37

View

Reel

₹462.68

Min.: 1
Mult.: 1

Reel: 2,500

RF System on a Chip - SoC

SMD/SMT

QFN-32

ARM Cortex M4

32 bit

40 MHz

256 kB

32 kB

12 bit

16 I/O

- 40 C

+ 85 C

Reel, Cut Tape

RF System on a Chip - SoC

SD3503A-CNE3R
Silicon Labs
1: ₹949.61
3,900In Stock
NRND

Mfr. Part No.
SD3503A-CNE3R

Mouser Part No
634-SD3503ACNE3R

NRND

Silicon Labs

RF System on a Chip - SoC

Datasheet

3,900In Stock

Cut Tape

₹949.61

₹848.99

₹809.46

₹702.55

View

Reel

₹508.49

Min.: 1
Mult.: 1

Reel: 2,000

RF System on a Chip - SoC

8051

128 kB

- 40 C

+ 90 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB LFO 8-bit MCU

C8051F338-GMR
Silicon Labs
1: ₹1,022.38
2,731In Stock

Mfr. Part No.
C8051F338-GMR

Mouser Part No
634-C8051F338-GMR

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB LFO 8-bit MCU

Datasheet

2,731In Stock

Cut Tape

₹1,022.38

₹917.27

₹875.04

₹759.15

View

Reel

₹563.30

MouseReel Available

Min.: 1
Mult.: 1

Reel: 1,500

8-bit Microcontrollers - MCU

SMD/SMT

QFN-24

8051

8 bit

25 MHz

16 kB

768 B

10 bit

21 I/O

- 40 C

+ 85 C

Reel, Cut Tape, MouseReel

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 16 kB flash 1.28 kB RAM 25 GPIO BB5 8-bit MCU

EFM8BB52F16G-C-TSSOP28
Silicon Labs
1: ₹79.96
8,368In Stock

Mfr. Part No.
EFM8BB52F16G-C-TSSOP28

Mouser Part No
634-EFM852F16GTSOP28

Silicon Labs

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 16 kB flash 1.28 kB RAM 25 GPIO BB5 8-bit MCU

Learn More

Datasheet

8,368In Stock

₹79.96

₹68.19

₹59.83

₹56.51

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

TSSOP-28

16 kB

1.28 kB

25 I/O

- 40 C

+ 85 C

Cut Tape

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB flash 2 kB RAM 8-bit Universal Bee MCU

EFM8UB10F16G-C-QFN20
Silicon Labs
1: ₹185.07
2,030In Stock

Mfr. Part No.
EFM8UB10F16G-C-QFN20

Mouser Part No
634-8UB10F16GCQFN20

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB flash 2 kB RAM 8-bit Universal Bee MCU

Datasheet

2,030In Stock

₹185.07

₹155.42

₹144.64

₹127.57

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

CIP-51 8051

8 bit

50 MHz

16 kB

2.25 kB

12 bit

13 I/O

- 40 C

+ 85 C

Tube

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB flash 2 kB RAM 8-bit Universal Bee MCU

EFM8UB10F16G-C-QFN28R
Silicon Labs
1: ₹194.95
7,593In Stock

Mfr. Part No.
EFM8UB10F16G-C-QFN28R

Mouser Part No
634-8UB10F16GCQFN28R

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB flash 2 kB RAM 8-bit Universal Bee MCU

Datasheet

7,593In Stock

Cut Tape

₹194.95

₹163.51

₹151.83

₹135.66

Reel

₹106.91

View

Min.: 1
Mult.: 1

Reel: 1,500

8-bit Microcontrollers - MCU

SMD/SMT

QFN-28

CIP-51 8051

8 bit

50 MHz

16 kB

2.25 kB

12 bit

22 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 8051 50 MHz 128 kB 5 V 8-bit MCU

C8051F581-IQ
Silicon Labs
1: ₹1,248.78
1,226In Stock

Mfr. Part No.
C8051F581-IQ

Mouser Part No
634-C8051F581-IQ

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 128 kB 5 V 8-bit MCU

Learn More

Datasheet

1,226In Stock

₹1,248.78

₹1,034.96

₹966.68

₹884.03

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFP-48

8051

8 bit

50 MHz

128 kB

8.25 kB

12 bit

40 I/O

- 40 C

+ 125 C

AEC-Q100

Tray

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 8 kB flash 1.28 kB RAM 16 GPIO BB5 8-bit MCU

EFM8BB51F8G-C-QFN20R
Silicon Labs
1: ₹64.68
9,875In Stock

Mfr. Part No.
EFM8BB51F8G-C-QFN20R

Mouser Part No
634-EFM851F8GCQFN20R

Silicon Labs

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 8 kB flash 1.28 kB RAM 16 GPIO BB5 8-bit MCU

Learn More

Datasheet

9,875In Stock

Cut Tape

₹64.68

₹55.52

₹51.66

₹46.09

Reel

₹34.32

View

Min.: 1
Mult.: 1

Reel: 2,500

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

16 kB

1.28 kB

16 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 16 kB flash 1.28 kB RAM 16 GPIO BB5 8-bit MCU

EFM8BB51F16G-C-QFN20R
Silicon Labs
1: ₹132.96
6,565In Stock

Mfr. Part No.
EFM8BB51F16G-C-QFN20R

Mouser Part No
634-EFM851F16GQFN20R

Silicon Labs

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 16 kB flash 1.28 kB RAM 16 GPIO BB5 8-bit MCU

Learn More

Datasheet

6,565In Stock

Cut Tape

₹132.96

₹85.17

₹76.00

₹62.53

Reel

₹39.62

View

Min.: 1
Mult.: 1

Reel: 2,500

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

16 kB

1.28 kB

16 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 32 kB flash 2.304 kB RAM 29 GPIO BB5 8-bit MCU

EFM8BB52F32I-C-QFN32R
Silicon Labs
1: ₹151.83
13,390In Stock

Mfr. Part No.
EFM8BB52F32I-C-QFN32R

Mouser Part No
634-EFM852F32IQFN32R

Silicon Labs

8-bit Microcontrollers - MCU 5 Volt 8051 50 Mhz 32 kB flash 2.304 kB RAM 29 GPIO BB5 8-bit MCU

Learn More

Datasheet

13,390In Stock

Cut Tape

₹151.83

₹97.03

₹86.25

₹70.97

Reel

₹43.75

View

Min.: 1
Mult.: 1

Reel: 2,500

8-bit Microcontrollers - MCU

SMD/SMT

QFN-32

16 kB

1.28 kB

16 I/O

- 40 C

+ 85 C

Reel, Cut Tape

8-bit Microcontrollers - MCU 8051 25 MHz 64 kB CAN 8-bit MCU

C8051F040-GQ
Silicon Labs
1: ₹1,960.31
301In Stock
NRND

Mfr. Part No.
C8051F040-GQ

Mouser Part No
634-C8051F040-GQ

NRND

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 64 kB CAN 8-bit MCU

Datasheet

301In Stock

₹1,960.31

₹1,729.42

₹1,698.87

₹1,697.98

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

TQFP-100

8051

8 bit

25 MHz

64 kB

4.25 kB

8 bit, 12 bit

64 I/O

- 40 C

+ 85 C

Tray

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

EFM8BB21F16I-C-QFN20
Silicon Labs
1: ₹123.98
4,859In Stock

Mfr. Part No.
EFM8BB21F16I-C-QFN20

Mouser Part No
634-8BB21F16I-CQFN20

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

Learn More

Datasheet

4,859In Stock

₹123.98

₹105.11

₹97.93

₹85.62

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

CIP-51 8051

8 bit

50 MHz

16 kB

2.3 kB

12 bit

16 I/O

- 40 C

+ 125 C

Tube

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB LFO 8-bit MCU

C8051F336-GM
Silicon Labs
1: ₹652.24
3,490In Stock

Mfr. Part No.
C8051F336-GM

Mouser Part No
634-C8051F336-GM

Silicon Labs

8-bit Microcontrollers - MCU 8051 25 MHz 16 kB LFO 8-bit MCU

Datasheet

3,490In Stock

₹652.24

₹540.84

₹520.17

₹506.70

Quote

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-20

8051

8 bit

25 MHz

16 kB

768 B

10 bit

17 I/O

- 40 C

+ 85 C

Tube

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

EFM8BB31F16I-D-QFP32
Silicon Labs
1: ₹303.66
516In Stock

Mfr. Part No.
EFM8BB31F16I-D-QFP32

Mouser Part No
634-EF8BB31F16IDQP32

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

Learn More

Datasheet

516In Stock

₹303.66

₹200.34

₹185.07

₹160.81

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFP-32

CIP-51 8051

8 bit

50 MHz

16 kB

2.3 kB

10 bit, 12 bit

28 I/O

- 40 C

+ 125 C

Tray

8-bit Microcontrollers - MCU 8051 75 MHz 16 kB flash 1.25 kB RAM 8-bit Laser Bee MCU

EFM8LB10F16E-C-QFN32
Silicon Labs
1: ₹297.37
630In Stock

Mfr. Part No.
EFM8LB10F16E-C-QFN32

Mouser Part No
634-LB10F16ECQFN32

Silicon Labs

8-bit Microcontrollers - MCU 8051 75 MHz 16 kB flash 1.25 kB RAM 8-bit Laser Bee MCU

Learn More

Datasheet

630In Stock

₹297.37

₹194.05

₹177.88

₹152.73

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-32

CIP-51 8051

8 bit

72 MHz

16 kB

1.25 kB

10 bit/12 bit/14 bit

29 I/O

- 40 C

+ 105 C

Tray

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

EFM8BB22F16G-C-QFN28
Silicon Labs
1: ₹150.93
2,047In Stock

Mfr. Part No.
EFM8BB22F16G-C-QFN28

Mouser Part No
634-8BB22F16GCQFN28

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 16 kB flash 2.25 kB RAM 8-bit Busy Bee MCU

Learn More

Datasheet

2,047In Stock

₹150.93

₹127.57

₹108.71

₹102.42

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFN-28

CIP-51 8051

8 bit

50 MHz

16 kB

2.3 kB

12 bit

22 I/O

- 40 C

+ 85 C

Tube

8-bit Microcontrollers - MCU 8051 50 MHz 64 kB flash 4.25 kB RAM 8-bit Busy Bee MCU

EFM8BB31F64I-D-QFP32
Silicon Labs
1: ₹407.87
164In Stock

Mfr. Part No.
EFM8BB31F64I-D-QFP32

Mouser Part No
634-EF8BB31F64IDQP32

Silicon Labs

8-bit Microcontrollers - MCU 8051 50 MHz 64 kB flash 4.25 kB RAM 8-bit Busy Bee MCU

Datasheet

164In Stock

₹407.87

₹271.32

₹250.65

₹218.31

View

Min.: 1
Mult.: 1

8-bit Microcontrollers - MCU

SMD/SMT

QFP-32

CIP-51 8051

8 bit

50 MHz

64 kB

4.35 kB

10 bit, 12 bit

28 I/O

- 40 C

+ 125 C

Tray

RF System on a Chip - SoC Blue Gecko, QFN32, 2.4G, 6dB, Bluetooth 5.2, 352kB, 32kB(RAM), 18 GPIO

EFR32BG22C222F352GM32-CR
Silicon Labs
1: ₹337.80
15In Stock
2,500Expected 13-03-2026

Mfr. Part No.
EFR32BG22C222F352GM32-CR

Mouser Part No
634-ER32BG22352GM3CR

Silicon Labs

RF System on a Chip - SoC Blue Gecko, QFN32, 2.4G, 6dB, Bluetooth 5.2, 352kB, 32kB(RAM), 18 GPIO

Learn More

Datasheet

15In Stock

2,500Expected 13-03-2026

Cut Tape

₹337.80

₹229.09

₹212.02

₹184.17

Reel

₹115.89

View

Min.: 1
Mult.: 1

Reel: 2,500

RF System on a Chip - SoC

SMD/SMT

QFN-32

ARM Cortex M33

32 bit

76.8 MHz

352 kB

32 kB

12 bit

18 I/O

- 40 C

+ 85 C

Reel, Cut Tape

Silicon Labs Embedded Processors & Controllers

Types of Embedded Processors & Controllers

Customer Service Office

Company

Resources

Support

BGA-112
BGA-120
BGA-125
BGA-136
BGA-152
BGA-192
BGA-48
CSP-16
CSP-43
CSP-81
LGA-42
LGA-85
LGA-92
LQFP-100
LQFP-32
MSOP-10
PQFP-48
QFN-11
QFN-12
QFN-16

5 MHz
12 MHz
24 MHz
24.5 MHz
25 MHz
32 MHz
38.4 MHz
39 MHz
40 MHz
48 MHz
50 MHz
72 MHz
76.8 MHz
78 MHz
80 MHz
97.5 MHz
100 MHz
150 MHz
180 MHz
2.4 GHz

1.5 kB
2 kB
4 kB
8 kB
16 kB
32 kB
64 kB
96 kB
128 kB
192 kB
256 kB
352 kB
512 kB
768 kB
1 MB
1.02 MB
1024 kB
1152 kB
1.5 MB
1536 kB

8 B, 256 B, 4 kB
128 B
256 B
512 B
768 B
1 kB
1.25 kB
1.28 kB
1.54 kB
2 kB
2.25 kB
2.3 kB
2.31 kB
3.25 kB
4 kB
4 kB, 256 B, 8 B
4.25 kB
4.35 kB
4352 B
8 kB

5 I/O
6 I/O
8 I/O
9 I/O
11 I/O
12 I/O
13 I/O
15 I/O
16 I/O
17 I/O
18 I/O
19 I/O
20 I/O
21 I/O
22 I/O
23 I/O
24 I/O
25 I/O
26 I/O
27 I/O