ZHCSGV3G June   2009  – January 2017 TMS320C6748

PRODUCTION DATA.  

  1. 1器件概述
    1. 1.1 特性
    2. 1.2 应用
    3. 1.3 说明
    4. 1.4 功能方框图
  2. 2Revision History
  3. 3Device Comparison
    1. 3.1 Device Characteristics
    2. 3.2 Device Compatibility
    3. 3.3 DSP Subsystem
      1. 3.3.1 C674x DSP CPU Description
      2. 3.3.2 DSP Memory Mapping
        1. 3.3.2.1 External Memories
        2. 3.3.2.2 DSP Internal Memories
        3. 3.3.2.3 C674x CPU
    4. 3.4 Memory Map Summary
      1. Table 3-4 C6748 Top Level Memory Map
    5. 3.5 Pin Assignments
      1. 3.5.1 Pin Map (Bottom View)
    6. 3.6 Pin Multiplexing Control
    7. 3.7 Terminal Functions
      1. 3.7.1  Device Reset, NMI and JTAG
      2. 3.7.2  High-Frequency Oscillator and PLL
      3. 3.7.3  Real-Time Clock and 32-kHz Oscillator
      4. 3.7.4  DEEPSLEEP Power Control
      5. 3.7.5  External Memory Interface A (EMIFA)
      6. 3.7.6  DDR2/mDDR Controller
      7. 3.7.7  Serial Peripheral Interface Modules (SPI)
      8. 3.7.8  Programmable Real-Time Unit (PRU)
      9. 3.7.9  Enhanced Capture/Auxiliary PWM Modules (eCAP0)
      10. 3.7.10 Enhanced Pulse Width Modulators (eHRPWM)
      11. 3.7.11 Boot
      12. 3.7.12 Universal Asynchronous Receiver/Transmitters (UART0, UART1, UART2)
      13. 3.7.13 Inter-Integrated Circuit Modules(I2C0, I2C1)
      14. 3.7.14 Timers
      15. 3.7.15 Multichannel Audio Serial Ports (McASP)
      16. 3.7.16 Multichannel Buffered Serial Ports (McBSP)
      17. 3.7.17 Universal Serial Bus Modules (USB0, USB1)
      18. 3.7.18 Ethernet Media Access Controller (EMAC)
      19. 3.7.19 Multimedia Card/Secure Digital (MMC/SD)
      20. 3.7.20 Liquid Crystal Display Controller(LCD)
      21. 3.7.21 Serial ATA Controller (SATA)
      22. 3.7.22 Universal Host-Port Interface (UHPI)
      23. 3.7.23 Universal Parallel Port (uPP)
      24. 3.7.24 Video Port Interface (VPIF)
      25. 3.7.25 General Purpose Input Output
      26. 3.7.26 Reserved and No Connect
      27. 3.7.27 Supply and Ground
    8. 3.8 Unused Pin Configurations
  4. 4Device Configuration
    1. 4.1 Boot Modes
    2. 4.2 SYSCFG Module
    3. 4.3 Pullup/Pulldown Resistors
  5. 5Specifications
    1. 5.1 Absolute Maximum Ratings Over Operating Junction Temperature Range (Unless Otherwise Noted)
    2. 5.2 Handling Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Notes on Recommended Power-On Hours (POH)
    5. 5.5 Electrical Characteristics Over Recommended Ranges of Supply Voltage and Operating Junction Temperature (Unless Otherwise Noted)
  6. 6Peripheral Information and Electrical Specifications
    1. 6.1  Parameter Information
      1. 6.1.1 Parameter Information Device-Specific Information
        1. 6.1.1.1 Signal Transition Levels
    2. 6.2  Recommended Clock and Control Signal Transition Behavior
    3. 6.3  Power Supplies
      1. 6.3.1 Power-On Sequence
      2. 6.3.2 Power-Off Sequence
    4. 6.4  Reset
      1. 6.4.1 Power-On Reset (POR)
      2. 6.4.2 Warm Reset
      3. 6.4.3 Reset Electrical Data Timings
    5. 6.5  Crystal Oscillator or External Clock Input
    6. 6.6  Clock PLLs
      1. 6.6.1 PLL Device-Specific Information
      2. 6.6.2 Device Clock Generation
      3. 6.6.3 Dynamic Voltage and Frequency Scaling (DVFS)
    7. 6.7  Interrupts
      1. 6.7.1 DSP Interrupts
    8. 6.8  Power and Sleep Controller (PSC)
      1. 6.8.1 Power Domain and Module Topology
        1. 6.8.1.1 Power Domain States
        2. 6.8.1.2 Module States
    9. 6.9  Enhanced Direct Memory Access Controller (EDMA3)
      1. 6.9.1 EDMA3 Channel Synchronization Events
      2. 6.9.2 EDMA3 Peripheral Register Descriptions
    10. 6.10 External Memory Interface A (EMIFA)
      1. 6.10.1 EMIFA Asynchronous Memory Support
      2. 6.10.2 EMIFA Synchronous DRAM Memory Support
      3. 6.10.3 EMIFA SDRAM Loading Limitations
      4. 6.10.4 EMIFA Connection Examples
      5. 6.10.5 External Memory Interface Register Descriptions
      6. 6.10.6 EMIFA Electrical Data/Timing
        1. Table 6-19 Timing Requirements for EMIFA SDRAM Interface
        2. Table 6-20 Switching Characteristics for EMIFA SDRAM Interface
        3. Table 6-21 Timing Requirements for EMIFA Asynchronous Memory Interface
    11. 6.11 DDR2/mDDR Memory Controller
      1. 6.11.1 DDR2/mDDR Memory Controller Electrical Data/Timing
      2. 6.11.2 DDR2/mDDR Memory Controller Register Description(s)
      3. 6.11.3 DDR2/mDDR Interface
        1. 6.11.3.1  DDR2/mDDR Interface Schematic
        2. 6.11.3.2  Compatible JEDEC DDR2/mDDR Devices
        3. 6.11.3.3  PCB Stackup
        4. 6.11.3.4  Placement
        5. 6.11.3.5  DDR2/mDDR Keep Out Region
        6. 6.11.3.6  Bulk Bypass Capacitors
        7. 6.11.3.7  High-Speed Bypass Capacitors
        8. 6.11.3.8  Net Classes
        9. 6.11.3.9  DDR2/mDDR Signal Termination
        10. 6.11.3.10 VREF Routing
        11. 6.11.3.11 DDR2/mDDR CK and ADDR_CTRL Routing
        12. 6.11.3.12 DDR2/mDDR Boundary Scan Limitations
    12. 6.12 Memory Protection Units
    13. 6.13 MMC / SD / SDIO (MMCSD0, MMCSD1)
      1. 6.13.1 MMCSD Peripheral Description
      2. 6.13.2 MMCSD Peripheral Register Description(s)
      3. 6.13.3 MMC/SD Electrical Data/Timing
        1. Table 6-40 Timing Requirements for MMC/SD (see and )
        2. Table 6-41 Switching Characteristics for MMC/SD (see through )
    14. 6.14 Serial ATA Controller (SATA)
      1. 6.14.1 SATA Register Descriptions
      2. 6.14.2 1. SATA Interface
        1. 6.14.2.1 SATA Interface Schematic
        2. 6.14.2.2 Compatible SATA Components and Modes
        3. 6.14.2.3 PCB Stackup Specifications
        4. 6.14.2.4 Routing Specifications
        5. 6.14.2.5 Coupling Capacitors
        6. 6.14.2.6 SATA Interface Clock Source requirements
      3. 6.14.3 SATA Unused Signal Configuration
    15. 6.15 Multichannel Audio Serial Port (McASP)
      1. 6.15.1 McASP Peripheral Registers Description(s)
      2. 6.15.2 McASP Electrical Data/Timing
        1. 6.15.2.1 Multichannel Audio Serial Port 0 (McASP0) Timing
          1. Table 6-52 Timing Requirements for McASP0 (1.3V, 1.2V, 1.1V)
          2. Table 6-53 Timing Requirements for McASP0 (1.0V)
          3. Table 6-54 Switching Characteristics for McASP0 (1.3V, 1.2V, 1.1V)
          4. Table 6-55 Switching Characteristics for McASP0 (1.0V)
    16. 6.16 Multichannel Buffered Serial Port (McBSP)
      1. 6.16.1 McBSP Peripheral Register Description(s)
      2. 6.16.2 McBSP Electrical Data/Timing
        1. 6.16.2.1 Multichannel Buffered Serial Port (McBSP) Timing
          1. Table 6-57 Timing Requirements for McBSP0 [1.3V, 1.2V, 1.1V] (see )
          2. Table 6-58 Timing Requirements for McBSP0 [1.0V] (see )
          3. Table 6-59 Switching Characteristics for McBSP0 [1.3V, 1.2V, 1.1V] (see )
          4. Table 6-60 Switching Characteristics for McBSP0 [1.0V] (see )
          5. Table 6-61 Timing Requirements for McBSP1 [1.3V, 1.2V, 1.1V] (see )
          6. Table 6-62 Timing Requirements for McBSP1 [1.0V] (see )
          7. Table 6-63 Switching Characteristics for McBSP1 [1.3V, 1.2V, 1.1V] (see )
          8. Table 6-64 Switching Characteristics for McBSP1 [1.0V] (see )
          9. Table 6-65 Timing Requirements for McBSP0 FSR When GSYNC = 1 (see )
          10. Table 6-66 Timing Requirements for McBSP1 FSR When GSYNC = 1 (see )
    17. 6.17 Serial Peripheral Interface Ports (SPI0, SPI1)
      1. 6.17.1 SPI Peripheral Registers Description(s)
      2. 6.17.2 SPI Electrical Data/Timing
        1. 6.17.2.1 Serial Peripheral Interface (SPI) Timing
          1. Table 6-68 General Timing Requirements for SPI0 Master Modes
          2. Table 6-69 General Timing Requirements for SPI0 Slave Modes
          3. Table 6-76 General Timing Requirements for SPI1 Master Modes
          4. Table 6-77 General Timing Requirements for SPI1 Slave Modes
          5. Table 6-78 Additional SPI1 Master Timings, 4-Pin Enable Option
          6. Table 6-79 Additional SPI1 Master Timings, 4-Pin Chip Select Option
    18. 6.18 Inter-Integrated Circuit Serial Ports (I2C)
      1. 6.18.1 I2C Device-Specific Information
      2. 6.18.2 I2C Peripheral Registers Description(s)
      3. 6.18.3 I2C Electrical Data/Timing
        1. 6.18.3.1 Inter-Integrated Circuit (I2C) Timing
          1. Table 6-85 Timing Requirements for I2C Input
          2. Table 6-86 Switching Characteristics for I2C
    19. 6.19 Universal Asynchronous Receiver/Transmitter (UART)
      1. 6.19.1 UART Peripheral Registers Description(s)
      2. 6.19.2 UART Electrical Data/Timing
        1. Table 6-88 Timing Requirements for UART Receive (see )
        2. Table 6-89 Switching Characteristics Over Recommended Operating Conditions for UARTx Transmit (see )
    20. 6.20 Universal Serial Bus OTG Controller (USB0) [USB2.0 OTG]
      1. 6.20.1 USB0 [USB2.0] Electrical Data/Timing
        1. Table 6-91 Switching Characteristics Over Recommended Operating Conditions for USB0 [USB2.0] (see )
    21. 6.21 Universal Serial Bus Host Controller (USB1) [USB1.1 OHCI]
      1. Table 6-93 Switching Characteristics Over Recommended Operating Conditions for USB1 [USB1.1]
    22. 6.22 Ethernet Media Access Controller (EMAC)
      1. 6.22.1 EMAC Peripheral Register Description(s)
        1. 6.22.1.1 EMAC Electrical Data/Timing
          1. Table 6-98   Timing Requirements for MII_RXCLK (see )
          2. Table 6-99   Timing Requirements for MII_TXCLK (see )
          3. Table 6-100 Timing Requirements for EMAC MII Receive 10/100 Mbit/s (see )
          4. Table 6-101 Switching Characteristics Over Recommended Operating Conditions for EMAC MII Transmit 10/100 Mbit/s (see )
    23. 6.23 Management Data Input/Output (MDIO)
      1. 6.23.1 MDIO Register Description(s)
      2. 6.23.2 Management Data Input/Output (MDIO) Electrical Data/Timing
        1. Table 6-105 Timing Requirements for MDIO Input (see and )
        2. Table 6-106 Switching Characteristics Over Recommended Operating Conditions for MDIO Output (see )
    24. 6.24 LCD Controller (LCDC)
      1. 6.24.1 LCD Interface Display Driver (LIDD Mode)
      2. 6.24.2 LCD Raster Mode
        1. Table 6-110 Switching Characteristics Over Recommended Operating Conditions for LCD Raster Mode
    25. 6.25 Host-Port Interface (UHPI)
      1. 6.25.1 HPI Device-Specific Information
      2. 6.25.2 HPI Peripheral Register Description(s)
      3. 6.25.3 HPI Electrical Data/Timing
        1. Table 6-112 Timing Requirements for Host-Port Interface [1.2V, 1.1V]
        2. Table 6-113 Switching Characteristics Over Recommended Operating Conditions for Host-Port Interface [1.3V, 1.2V, 1.1V]
        3. Table 6-114 Switching Characteristics Over Recommended Operating Conditions for Host-Port Interface [1.0V]
    26. 6.26 Universal Parallel Port (uPP)
      1. 6.26.1 uPP Register Descriptions
        1. Table 6-115 Universal Parallel Port (uPP) Registers
      2. 6.26.2 uPP Electrical Data/Timing
        1. Table 6-116 Timing Requirements for uPP (see , , , )
        2. Table 6-117 Switching Characteristics Over Recommended Operating Conditions for uPP
    27. 6.27 Video Port Interface (VPIF)
      1. 6.27.1 VPIF Register Descriptions
        1. Table 6-118 Video Port Interface (VPIF) Registers
      2. 6.27.2 VPIF Electrical Data/Timing
        1. Table 6-119 Timing Requirements for VPIF VP_CLKINx Inputs (see )
        2. Table 6-120 Timing Requirements for VPIF Channels 0/1 Video Capture Data and Control Inputs (see )
        3. Table 6-121 Switching Characteristics Over Recommended Operating Conditions for Video Data Shown With Respect to VP_CLKOUT2/3 (see )
    28. 6.28 Enhanced Capture (eCAP) Peripheral
      1. Table 6-123 Timing Requirements for Enhanced Capture (eCAP)
      2. Table 6-124 Switching Characteristics Over Recommended Operating Conditions for eCAP
    29. 6.29 Enhanced High-Resolution Pulse-Width Modulator (eHRPWM)
      1. 6.29.1 Enhanced Pulse Width Modulator (eHRPWM) Timing
        1. Table 6-126 Timing Requirements for eHRPWM
        2. Table 6-127 Switching Characteristics Over Recommended Operating Conditions for eHRPWM
      2. 6.29.2 Trip-Zone Input Timing
    30. 6.30 Timers
      1. 6.30.1 Timer Electrical Data/Timing
        1. Table 6-130 Timing Requirements for Timer Input (see )
        2. Table 6-131 Switching Characteristics Over Recommended Operating Conditions for Timer Output
    31. 6.31 Real Time Clock (RTC)
      1. 6.31.1 Clock Source
      2. 6.31.2 Real-Time Clock Register Descriptions
    32. 6.32 General-Purpose Input/Output (GPIO)
      1. 6.32.1 GPIO Register Description(s)
      2. 6.32.2 GPIO Peripheral Input/Output Electrical Data/Timing
        1. Table 6-134 Timing Requirements for GPIO Inputs (see )
        2. Table 6-135 Switching Characteristics Over Recommended Operating Conditions for GPIO Outputs (see )
      3. 6.32.3 GPIO Peripheral External Interrupts Electrical Data/Timing
        1. Table 6-136 Timing Requirements for External Interrupts (see )
    33. 6.33 Programmable Real-Time Unit Subsystem (PRUSS)
      1. 6.33.1 PRUSS Register Descriptions
    34. 6.34 Emulation Logic
      1. 6.34.1 JTAG Port Description
      2. 6.34.2 Scan Chain Configuration Parameters
      3. 6.34.3 Initial Scan Chain Configuration
      4. 6.34.4 IEEE 1149.1 JTAG
        1. 6.34.4.1 JTAG Peripheral Register Description(s) – JTAG ID Register (DEVIDR0)
        2. 6.34.4.2 JTAG Test-Port Electrical Data/Timing
          1. Table 6-147 Timing Requirements for JTAG Test Port (see )
          2. Table 6-148 Switching Characteristics Over Recommended Operating Conditions for JTAG Test Port (see )
      5. 6.34.5 JTAG 1149.1 Boundary Scan Considerations
  7. 7Device and Documentation Support
    1. 7.1 Device Nomenclature
    2. 7.2 Tools and Software
    3. 7.3 Documentation Support
    4. 7.4 社区资源
    5. 7.5 商标
    6. 7.6 静电放电警告
    7. 7.7 出口管制提示
    8. 7.8 术语表
  8. 8Mechanical Packaging and Orderable Information
    1. 8.1 Thermal Data for ZCE Package
    2. 8.2 Thermal Data for ZWT Package
    3. 8.3 Packaging Information

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)
  • ZCE|361
  • ZWT|361
散热焊盘机械数据 (封装 | 引脚)
订购信息

特性

  • 375MHz 和 456MHz C674x 定点和浮点超长指令字 (VLIW) 数字信号处理器 (DSP)
  • C674x 指令集 特性
    • C67x+ 和 C64x+ ISA 的超集
    • 高达 3648 MIPS 和 2746 MFLOPS
    • 可按字节寻址(8 位、16 位、32 位和 64 位数据)
    • 8 位溢出保护
    • 位域提取、设定、清空
    • 正常化、饱和、位计数
    • 紧凑 16 位指令
  • C674x 二级缓存架构
    • 32KB 的 L1P 程序 RAM/缓存
    • 32KB 的 L1D 数据 RAM/缓存
    • 256KB 的 L2 统一映射 RAM/缓存
    • 灵活 RAM/缓存分区(L1 和 L2)
  • 增强型直接存储器访问控制器 3 (EDMA3):
    • 2 个通道控制器
    • 3 个传输控制器
    • 64 个独立 DMA 通道
    • 16 个快速 DMA 通道
    • 可编程传输突发尺寸
  • TMS320C674x 浮点 VLIW DSP 内核
    • 具备非对齐支持的 Load-Store 架构
    • 64 个通用寄存器(32 位)
    • 6 个 ALU(32 位和 40 位)功能单元
      • 支持 32 位整型,SP(IEEE 单精度/32 位)和 DP(IEEE 双精度/64 位)浮点数
      • 每个时钟支持多达 4 次 SP 加法,每 2 个时钟支持多达 4 次 DP 加法
      • 每个周期支持多达 2 次浮点数(SP 或 DP)倒数逼近 (RCPxP) 和平方根倒数逼近 (RSQRxP) 运算
    • 2 个乘法功能单元:
      • 混合精度 IEEE 浮点乘法支持高达:
        • 每时钟 2 次 SP × SP → SP 运算
        • 每 2 个时钟 2 次 SP × SP → DP 运算
        • 每 3 个时钟 2 次 SP × DP → DP 运算
        • 每 4 个时钟 2 次 DP × DP → DP 运算
      • 定点乘法每个时钟周期支持 2 次 32 × 32 位乘法、4 次 16 × 16 位乘法或 8 次 8 × 8 位乘法,而且还支持复杂的乘法
    • 指令压缩减少代码尺寸
    • 所有指令所需条件
    • 取模循环运算的硬件支持
    • 受保护模式运行
    • 对于错误检测和程序重定向的额外支持
  • 软件支持
    • TI DSPBIOS™
    • 芯片支持库和 DSP 库
  • 128KB 的 RAM 共享存储器
  • 1.8V 或 3.3V LVCMOS I/O(USB 和 DDR2 接口除外)
  • 2 个外部存储器接口:
    • EMIFA
      • NOR(8 位宽或 16 位宽数据)
      • NAND(8 位宽或 16 位宽数据)
      • 具有 128MB 地址空间的 16 位 SDRAM
    • DDR2/移动 DDR 存储器控制器,有以下两种选项:
      • 具有 256MB 地址空间的 16 位 DDR2 SDRAM
      • 具有 256MB 地址空间的 16 位 mDDR SDRAM
  • 3 个可配置的 16550 型 UART 模块:
    • 含调制解调器控制信号
    • 16 字节 FIFO
    • 16x 或 13x 过采样选项
  • LCD 控制器
  • 2 个串行外设接口 (SPI),每个接口都有多个芯片选择
  • 2 个多媒体卡 (MMC)/安全数字 (SD) 卡接口,具有安全数据 I/O (SDIO) 接口
  • 2 个主/从内部集成电路
    (I2C Bus™)
  • 1 个主机端口接口 (HPI),通过 16 位宽的多路复用地址和数据总线实现高带宽
  • 可编程实时单元子系统 (PRUSS)
    • 2 个独立的可编程实时单元 (PRU) 内核
      • 32 位 Load-Store 精简指令集计算机 (RISC) 架构
      • 每个内核 4KB 的指令 RAM
      • 每个内核 512 字节的数据 RAM
      • 可通过软件禁用 PRUSS 以实现节能
      • 除了 PRU 内核的正常 R31 输出,还会从子系统中导出每个 PRU 的寄存器 30。
    • 标准的电源管理机制
      • 时钟选通
      • 在一个单一 PSC 时钟选通域下的完整子系统
    • 专用中断控制器
    • 专用开关中心源
  • 具有集成型 PHY 的 USB 1.1 OHCI (主机) (USB1)
  • 具有集成型 PHY 的 USB 2.0 OTG 端口 (USB0)
    • USB 2.0 高速和全速客户端
    • USB 2.0 高速、全速和低速主机
    • 端点 0(控制)
    • 端点 1、2、3 和 4(控制、批量、中断或 ISOC)RX 和 TX
  • 1 个多通道音频串行端口 (McASP):
    • 2 个时钟域和 16 个串行数据引脚
    • 支持时分复用 (TDM),I2S,和相似格式
    • 支持动态互联网技术 (DIT)
    • 用于发送和接收的 FIFO 缓冲器
  • 2 个多通道缓冲串行端口 (McBSP):
    • 支持 TDM,I2S,和相似格式
    • AC97 音频编解码器接口
    • 电信接口(ST 总线,H100)
    • 128 通道时分复用 (TDM)
    • 用于发送和接收的 FIFO 缓冲器
  • 10/100Mbps 以太网 MAC (EMAC):
    • 符合 IEEE 802.3 标准
    • MII 介质独立接口
    • RMII 简化的介质独立接口
    • 管理数据 I/O (MDIO) 模块
  • 视频端口接口 (VPIF):
    • 2 个 8 位 SD (BT.656)、单个 16 位或单个原始(8 位、10 位和 12 位)视频捕捉通道
    • 2 个 8 位 SD (BT.656)、单个 16 位视频显示通道
  • 通用并行端口 (uPP):
    • 到现场可编门阵列 (FPGA) 和数据转换器的高速并行接口
    • 两个通道的数据宽度为 8 位至 16 位(包括 8 位和 16 位)
    • 单倍数据速率或双倍数据速率传输
    • 支持具有 START、ENABLE 和 WAIT(开始、使能和等待)控制的多个接口
  • 串行高级技术附件 (SATA) 控制器:
    • 支持 SATA I (1.5Gbps) 和 SATA II
      (3.0Gbps)
    • 支持全部 SATA 电源管理 特性
    • 高达 32 条的硬件辅助本地命令队列 (NCQ)
    • 支持端口复用器和基于命令的开关
  • 具有 32kHz 振荡器和独立电源轨的实时时钟 (RTC)
  • 3 个 64 位通用定时器(每一个可配置为 2 个 32 位定时器)
  • 1 个 64 位通用定时器或看门狗定时器(可配置为 2 个 32 位定时器)
  • 2 个增强的高分辨率脉宽调制器 (eHRPWM):
    • 具有周期和频率控制的专用 16 位时基计数器
    • 6 个单边沿输出、6 个双边沿对称输出或 3 个双边沿非对称输出
    • 死区生成
    • 高频载波实现的脉宽调制 (PWM) 斩波
    • 触发区输入
  • 3 个 32 位增强型捕捉 (eCAP) 模块:
    • 可配置为 3 个捕捉输入或 3 个辅助脉宽调制器 (APWM) 输出
    • 多达 4 个事件时间戳的单脉冲捕捉
  • 封装:
    • 361 焊球无铅塑封球栅阵列 (PBGA) [ZCE 后缀]、0.65mm 焊球间距
    • 361 焊球无铅 PBGA [ZWT 后缀]、
      0.80mm 焊球间距
  • 商业级、扩展级或工业级温度