SP3220EB参数引脚图艾科嘉现货供应价格EXAR-IC资料网

找IC，尽在114IC

登录注册

芯片资料

芯片资料
丝印反查
库存查询
行业新闻
制造商
替换型号
晶体管

精确

位置：首页 > IC中文资料第5467页 > SP3220EB

SP3220EB价格

参考价格：￥4.6103

型号：SP3220EBCA-L 品牌：Exar 备注：这里有SP3220EB多少钱，2026年最近7天走势，今日出价，今日竞价，SP3220EB批发/采购报价，SP3220EB行情走势销售排行榜，SP3220EB报价。

型号	功能描述	生产厂家企业	LOGO
SP3220EB	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EB	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EB	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EB	3.0V to 5.5V RS-232 1-driver/1-receiver with low-power shutdown The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver true RS-232 perfo ·Meets All EIA-232 and ITU V.28 Specifications from a wide +3.0V to +5.5V power supply·Interoperable with RS232 and V.28 at 2.7V·Supports High Serial Data Rates: 250kbps SP322·1μA Low Power Shutdown Mode·Footprint Compatible with MAX3221E, ISL3221·4 x 0.1μF External Charge Pump Capacitors·Tri–State/;	MAXLINEAR 迈凌	MAXLINEAR
SP3220EB	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EB	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：478.5 Kbytes Page：21 Pages	SIPEX	SIPEX
SP3220EBCA	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBCA-L	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBCA-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBCA-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBCA-LTR	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBCT	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBCT-L	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBCT-LTR	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBCY	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBCY-L	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBCY-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBCY-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEA	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBEA-L	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBEA-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEA-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEA-LTR	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBET	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBET-L	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBET-LTR	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBEY	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or hand-held applications such as palmtop computers, instrumentation and consumer products. These devices incorporate a high-efficiency charge-pump power supply that allows the SP3220E devices to deliver	SIPEX	SIPEX
SP3220EBEY-L	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBEY-L	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEY-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEY-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair FEATURES ■ Meets all EIA/TIA-232-F Standards from a +3.0V to +5.5V power supply • Interoperable with RS-232 and V.28 at +2.7V ■ Supports High Serial Data Rates: • 120kbps SP3220E • 250kbps SP3220EB • 1Mbps SP3220EU ■ 1μA Low Power Shutdown Mode ■ Footprint Compatible with MAX3221E, ISL322	MAXLINEAR 迈凌	MAXLINEAR
SP3220EBEY-LTR	3.0V to 5.5V RS-232 Driver/Receiver Pair DESCRIPTION The SP3220E devices are RS-232 driver/receiver solutions intended for portable or handheld applications such as palmtop computers, intrumentation and consumer products. These devices incorporate a high-efficiency, charge-pump power supply that allows the SP3220E devices to deliver tru	EXAR 艾科嘉	EXAR
SP3220EBCA	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBCA-L	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBCA-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBCA-L/TR	封装/外壳：16-SSOP（0.209"，5.30mm 宽）包装：卷带（TR）描述：IC TRANSCEIVER FULL 1/1 16SSOP 集成电路（IC）驱动器，接收器，收发器	ETC 知名厂家	ETC
SP3220EBCA-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBCT	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBCY	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBCY-L	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBCY-L	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBCY-L	封装/外壳：16-TSSOP（0.173"，4.40mm 宽）包装：卷带（TR）剪切带（CT）Digi-Reel® 得捷定制卷带描述：IC TRANSCEIVER FULL 1/1 16TSSOP 集成电路（IC）驱动器，接收器，收发器	ETC 知名厂家	ETC
SP3220EBCY-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBCY-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEA	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBEA-L	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEA-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEA-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEA-L-TR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBET	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBEY	High Speed 3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：165.99 Kbytes Page：19 Pages	SIPEX	SIPEX
SP3220EBEY-L	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEY-L/TR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
SP3220EBEY-LSLASHTR	3.0V to 5.5V RS-232 Driver/Receiver Pair 文件：446.07 Kbytes Page：20 Pages	EXAR 艾科嘉	EXAR
MA3220	Silicon planar type Silicon planar type For stabilization of power supply ■ Features • Mini type package (3-pin) • Allowing to achieve a high-density set • Sharp rising performance • Wide voltage range: VZ = 2.0 V to 36 V	PANASONIC 松下	PANASONIC
MA3220-L	Silicon planar type Silicon planar type For stabilization of power supply ■ Features • Mini type package (3-pin) • Allowing to achieve a high-density set • Sharp rising performance • Wide voltage range: VZ = 2.0 V to 36 V	PANASONIC 松下	PANASONIC
MA3220-M	Silicon planar type Silicon planar type For stabilization of power supply ■ Features • Mini type package (3-pin) • Allowing to achieve a high-density set • Sharp rising performance • Wide voltage range: VZ = 2.0 V to 36 V	PANASONIC 松下	PANASONIC
MAZ3220-H	Silicon planar type Silicon planar type For stabilization of power supply ■ Features • Mini type package (3-pin) • Allowing to achieve a high-density set • Sharp rising performance • Wide voltage range: VZ = 2.0 V to 36 V	PANASONIC 松下	PANASONIC
NTE3220	Optoisolator NPN Transistor Output Features: Current Transfer Ratio: CTR: 50 Min @ IF = 5mA, VCE = 5V High Input–Output Isolation Voltage: VISO = 5000Vrms Compact DIP Package: NTE3220: 2–Channel Type (8–Lead DIP) NTE3221: 4–Channel Type (16–Lead DIP) Applications: Computer Terminals System Ap	NTE	NTE

SP3220EB产品属性

类型
描述
型号
SP3220EB
制造商
SIPEX
制造商全称
Sipex Corporation
功能描述
+3.0V to +5.5V RS-232 Driver/Receiver Pair

SP3220EB供应商更多...

更新时间：2026-5-16 20:28:00

IC供应商	芯片型号	品牌	批号	封装	库存	备注	价格
深圳市华睿芯科技有限公司	SP3220EBCA	SIPEX	24+	SSOP16	20000	全新原厂原装，进口正品现货，正规渠道可含税！！	询价
深圳市明嘉莱科技有限公司	SP3220EBCA-L	SIPEX	20+	SMD	880000	明嘉莱只做原装正品现货	询价
深圳市昂芯微科技有限公司	SP3220EBEY-L/TR	SIPEX	23+	TSSOP	8800	只做原装正品现货	询价
深圳市亿联芯电子科技有限公司	SP3220EBCA-L	EXAR/艾科嘉	2023+	SSOP16	5037	一级代理优势现货,全新正品直营店	询价
深圳市东来宝电子科技有限公司	SP3220EBCA	EXAR/艾科嘉	24+	SSOP	39650	郑重承诺只做原装进口现货	询价
深圳市恒创达实业有限公司	SP3220EBCA-L	SIPEX	17+	SSOP	6200	100%原装正品现货	询价
深圳市赛美科科技有限公司	SP3220EBCA	SIPEX		SSOP-16	68500	一级代理原装正品假一罚十价格优势长期供货	询价
深圳市创新迹电子有限公司	SP3220EBC	SIPEX	22+	MSOP-16	20000	公司只有原装品质保障	询价
深圳市宇集芯电子有限公司	SP3220EBCA	SIPEX	25+	SSOP16	90000	一级代理商进口原装现货、假一罚十价格合理	询价
深圳市宏捷佳电子科技有限公司	SP3220EBCA	SPIEX	2024+	SSOP-16	50000	原装现货	询价

SP3220EB芯片相关品牌

SP3220EB规格书下载地址

SP3220EB参数引脚图相关

SP3220EB数据表相关新闻

SP3220EUEY-L
SP3220EUEY-L
2022-10-13
SP3072EEN-L/TR接口IC原装热卖
SP3072EEN-L/TR全新原装假一罚十！大量现货！价格优惠！欢迎新老客户来电咨询采购！
2019-10-31
SP3077EEN-L/TR接口IC原装热卖
SP3077EEN-L/TR全新原装假一罚十！大量现货！价格优惠！欢迎新老客户来电咨询采购！
2019-10-31
SP3078EEN-L/TR接口IC原装热卖
SP3078EEN-L/TR全新原装假一罚十！大量现货！价格优惠！欢迎新老客户来电咨询采购！
2019-10-30
SP3220EEY-L/TR接口集成电路原装热卖
SP3220EEY-L/TR全新原装假一罚十！大量现货！价格优惠！欢迎新老客户来电咨询采购！
2019-10-30
SP3223EEA-L/TR接口集成电路原装热卖
SP3223EEA-L/TR全新原装假一罚十！大量现货！价格优惠！欢迎新老客户来电咨询采购！
2019-10-30

DdatasheetPDF页码索引

P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
P21
P22
P23
P24
P25
P26
P27
P28
P29
P30
P31
P32
P33
P34
P35
P36
P37
P38
P39
P40
P41
P42
P43
P44
P45
P46
P47
P48
P49
P50
P51
P52
P53
P54
P55
P56
P57
P58
P59
P60
P61
P62
P63
P64
P65
P66
P67
P68
P69
P70
P71
P72
P73
P74
P75
P76
P77
P78
P79
P80
P81
P82
P83
P84
P85
P86
P87
P88
P89
P90
P91
P92
P93
P94
P95
P96
P97
P98
P99
P100
P101
P102
P103
P104
P105
P106
P107
P108
P109

找IC，尽在114IC

SP3220EB价格

SP3220EB产品属性

SP3220EB供应商更多...

SP3220EB芯片相关品牌

SP3220EB规格书下载地址

SP3220EB参数引脚图相关

SP3220EB数据表相关新闻

SP3220EUEY-L

SP3072EEN-L/TR接口IC原装热卖

SP3077EEN-L/TR接口IC原装热卖

SP3078EEN-L/TR接口IC原装热卖

SP3220EEY-L/TR接口集成电路原装热卖

SP3223EEA-L/TR接口集成电路原装热卖

DdatasheetPDF页码索引