类别是'category.RTCs(实时时钟)' (3750)
- 所有品牌
对比 | 图片 | 产品型号 | 品牌 | 数据表 | 库存 | 价格(含增值税) | 数量 | Rohs | 工厂交货时间 | 触点镀层 | 底架 | 安装类型 | 包装/外壳 | 表面安装 | 引脚数 | 供应商器件包装 | 操作温度 | 包装 | 已出版 | JESD-609代码 | 无铅代码 | 零件状态 | 湿度敏感性等级(MSL) | 终止次数 | ECCN 代码 | 类型 | 端子表面处理 | 最高工作温度 | 最小工作温度 | 附加功能 | HTS代码 | 电压 - 供电 | 端子位置 | 终端形式 | 峰值回流焊温度(摄氏度) | 电源电压 | 端子间距 | Reach合规守则 | 时间@峰值回流温度-最大值(s) | 基本部件号 | 引脚数量 | JESD-30代码 | 资历状况 | 工作电源电压 | 电源电压-最大值(Vsup) | 电源 | 温度等级 | 电源电压-最小值(Vsup) | 界面 | 最大电源电压 | 最小电源电压 | 内存大小 | uPs/uCs/外围ICs类型 | 比特数 | 时钟频率 | 逻辑功能 | 定时器数量 | 时间格式 | 日期格式 | 最大计时电流 | 时间-最小值 | 中断能力 | 电压 - 供电,电池 | 易失性 | 信息访问方法 | 特征 | 高度 | 座位高度(最大) | 长度 | 宽度 | 器件厚度 | 辐射硬化 | RoHS状态 | 无铅 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
![]() | X1288S16T1 | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 16-SOIC (0.295, 7.50mm Width) | 0°C~70°C | Tape & Reel (TR) | Obsolete | 1 (Unlimited) | Clock/Calendar | 4.5V~5.5V | X1288 | I2C, 2-Wire Serial | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 10μA~20μA @ 2.7V~5V | 1.8V~5.5V | Alarm, Leap Year, Supervisor, Watchdog Timer | Non-RoHS Compliant | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() | X1226V8IT2 | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 8-TSSOP (0.173, 4.40mm Width) | -40°C~85°C | Tape & Reel (TR) | Obsolete | 1 (Unlimited) | Clock/Calendar | 2.7V~5.5V | X1226 | I2C, 2-Wire Serial | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | 10μA~20μA @ 2.7V~5V | 1.8V~5.5V | Alarm, Leap Year | Non-RoHS Compliant | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() | ISL12021CVZ | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 14-TSSOP (0.173, 4.40mm Width) | 14-TSSOP | -20°C~70°C | Tube | Obsolete | 1 (Unlimited) | Clock/Calendar | 2.7V~5.5V | ISL12021 | I2C, 2-Wire Serial | 128B | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | 5.5μA~6.5μA @ 3V~5V | 1.8V~5.5V | Alarm, Daylight Savings, Leap Year, SRAM | ROHS3 Compliant | ||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() | X1286V14T1 | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 14-TSSOP (0.173, 4.40mm Width) | 0°C~70°C | Tape & Reel (TR) | Obsolete | 1 (Unlimited) | Clock/Calendar | 2.7V~5.5V | X1286 | I2C, 2-Wire Serial | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 10μA~20μA @ 2.7V~5V | 1.8V~5.5V | Alarm, Leap Year, Supervisor, Watchdog Timer | Non-RoHS Compliant | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() | X1288V14Z-2.7AT1 | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 14-TSSOP (0.173, 4.40mm Width) | 0°C~70°C | Tape & Reel (TR) | e3 | Obsolete | 2A (4 Weeks) | Clock/Calendar | Matte Tin (Sn) | 2.7V~5.5V | 未说明 | 未说明 | X1288 | I2C, 2-Wire Serial | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 10μA~20μA @ 2.7V~5V | 1.8V~5.5V | Alarm, Leap Year, Supervisor, Watchdog Timer | ROHS3 Compliant | ||||||||||||||||||||||||||||||||||||||||||||||||||
![]() | ISL12022MIBZ-T7A | Renesas Electronics America Inc. | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 20-SOIC (0.295, 7.50mm Width) | YES | -40°C~85°C | Tape & Reel (TR) | e3 | Obsolete | 1 (Unlimited) | 20 | Clock/Calendar | Matte Tin (Sn) - annealed | 2.7V~5.5V | DUAL | 1.27mm | ISL12022 | R-PDSO-G20 | 不合格 | 3/5V | I2C, 2-Wire Serial | 128B | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | 14μA~15μA @ 3V~5V | SECONDS | Y | 1.8V~5.5V | NO | SERIAL, 2 WIRE/I2C | Alarm, Daylight Savings, Leap Year, SRAM | Non-RoHS Compliant | ||||||||||||||||||||||||||||||||||||||||
![]() | MCP795B11T-I/ST | Microchip Technology | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | 14-TSSOP (0.173, 4.40mm Width) | YES | -40°C~85°C | Tape & Reel (TR) | 2011 | e3 | Obsolete | 1 (Unlimited) | 14 | EAR99 | Clock/Calendar | MATTE TIN (SN) | ALSO OPEARTES AT 1.8 V MINIMUM SUPPLY AT 3 MHZ | 8542.39.00.01 | 1.8V~5.5V | DUAL | 5V | 0.65mm | MCP795B11 | 14 | R-PDSO-G14 | 不合格 | 2/5V | SPI | 64B | 8 | 10MHz | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 1μA @ 1.8V~5.5V | 1/100SECOND | Y | 1.3V~5.5V | NO | Alarm, EEPROM, Leap Year, Square Wave Output, SRAM, Unique ID, Watchdog Timer | 1.2mm | 5mm | 4.4mm | ROHS3 Compliant | ||||||||||||||||||||||||||||||
![]() | DS1672S-3 T | Maxim Integrated | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | SOIC | YES | 8 | -40°C | e3 | yes | 1 (Unlimited) | 8 | EAR99 | 哑光锡 | DUAL | 鸥翼 | 260 | 3V | 1.27mm | 未说明 | 8 | 不合格 | 3.3V | 3V | INDUSTRIAL | 2.7V | TIMER, REAL TIME CLOCK | 0.032MHz | SECONDS | N | NO | I2C | 1.75mm | 4.9mm | 3.9mm | Non-RoHS Compliant | 无铅 | |||||||||||||||||||||||||||||||||||||
![]() | 1338C-31SRI | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | SOIC | 16 | Bulk | 2006 | e3 | no | Discontinued | 3 (168 Hours) | 16 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | 8542.39.00.01 | DUAL | 260 | 1.27mm | 16 | 3.3V | 5.5V | 3.6/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 56B | 0.032MHz | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | N | NO | I2C | 2.65mm | 10.4mm | 7.6mm | 2.34mm | 无 | 符合RoHS标准 | 含铅 | |||||||||||||||||||||||||||||
![]() | 1337DVGI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 6 Weeks | 表面贴装 | TSSOP | Tape & Reel (TR) | 2006 | e3 | yes | 3 (168 Hours) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | 8542.39.00.01 | DUAL | 260 | 3.3V | 0.65mm | 30 | 8 | R-PDSO-G8 | 3.3V | 5.5V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | Y | I2C | 1.1mm | 3mm | 3mm | 无 | 符合RoHS标准 | ||||||||||||||||||||||||||||||||
![]() | 1339-31DCGI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 7 Weeks | Tin | 表面贴装 | SOIC | 8 | Tape & Reel | 2006 | e3 | yes | 活跃 | 1 (Unlimited) | 8 | EAR99 | 85°C | -40°C | DUAL | 260 | 1.27mm | 30 | 8 | 不合格 | 3.3V | 5.5V | 3.6/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 0.032MHz | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | Y | YES | I2C | 1.75mm | 4.9mm | 3.9mm | 1.5mm | 符合RoHS标准 | 无铅 | |||||||||||||||||||||||||||||
![]() | 1337GDVGI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 7 Weeks | 表面贴装 | TSSOP | 8 | Tape & Reel | 2006 | 85°C | -40°C | 3.3V | 2-Wire, I2C, Serial | 5.5V | 1.8V | Clock | HH:MM:SS | YY-MM-DD-dd | 3mm | 3mm | 970μm | 无 | 符合RoHS标准 | 无铅 | |||||||||||||||||||||||||||||||||||||||||||||||||
![]() | 1337GNLGI | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | Tin | 表面贴装 | QFN | 16 | Bulk | 2006 | e3 | yes | Discontinued | 3 (168 Hours) | 16 | EAR99 | 85°C | -40°C | 8542.39.00.01 | QUAD | 260 | 3.3V | 0.5mm | 30 | 16 | 3.3V | 5.5V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 8 | 0.4MHz | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | Y | I2C | 3mm | 3mm | 1mm | 无 | 符合RoHS标准 | 无铅 | |||||||||||||||||||||||||||||
![]() | ISL12027IVAZ | Intersil (Renesas Electronics America) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | TSSOP | 8 | 2010 | e3 | 活跃 | 1 (Unlimited) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | DUAL | 260 | 3.3V | 0.65mm | 40 | 3.3V | 3/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 5.5V | 2.7V | 0.032MHz | Clock | HH:MM:SS | YY-MM-DD-dd | SECONDS | Y | NO | I2C | 1.2mm | 4.4mm | 3mm | 无 | 符合RoHS标准 | ||||||||||||||||||||||||||||||||||
![]() | ISL12027IV30AZ-T | Intersil (Renesas Electronics America) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | TSSOP | Tape & Reel | 2010 | e3 | 活跃 | 1 (Unlimited) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | 8542.39.00.01 | DUAL | 260 | 3.3V | 0.65mm | 40 | 8, 8 | R-PDSO-G8 | 3.3V | 3/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 5.5V | 2.7V | 0.032MHz | Clock | HH:MM:SS | YY-MM-DD-dd | SECONDS | Y | NO | I2C | 1.2mm | 4.4mm | 3mm | 无 | 符合RoHS标准 | |||||||||||||||||||||||||||||||
![]() | 1337DCGI | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | SOIC | 8 | 2006 | e3 | yes | 1 (Unlimited) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | DUAL | 260 | 3.3V | 1.27mm | 30 | 8 | 3.3V | 5.5V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | Y | I2C | 1.75mm | 4.9mm | 3.9mm | 无 | 符合RoHS标准 | |||||||||||||||||||||||||||||||||||
![]() | PT7C4311WEX | Pericom Semiconductor Corp. (Diodes Incorporated) | 数据表 | 4500 In Stock | - | 最小起订量: 1 最小包装量: 1 | YES | 85°C | -40°C | Tape & Reel (TR) | 8 | EAR99 | 8542.39.00.01 | DUAL | 鸥翼 | 2V | 1.27mm | compliant | 8 | R-PDSO-G8 | 不合格 | 5.5V | 1.8/5V | INDUSTRIAL | 1.5V | TIMER, REAL TIME CLOCK | 0.032MHz | 1 | SECONDS | N | NO | I2C | 1.75mm | 4.9mm | 3.9mm | 符合RoHS标准 | ||||||||||||||||||||||||||||||||||||||||
![]() | X1288V14 | Intersil (Renesas Electronics America) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | TSSOP | Bulk | 2005 | e0 | 1 (Unlimited) | 14 | EAR99 | Tin/Lead (Sn/Pb) | 70°C | 0°C | 8542.39.00.01 | DUAL | 240 | 5V | 0.65mm | 30 | 14 | R-PDSO-G14 | 不合格 | 5.5V | 5V | COMMERCIAL | 4.5V | 2-Wire, I2C, Serial | 31.3kB | TIMER, REAL TIME CLOCK | 0.032MHz | 1 | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 1/100SECOND | Y | YES | I2C | 1.2mm | 5mm | 4.4mm | 符合RoHS标准 | 含铅 | ||||||||||||||||||||||||||||||
![]() | X1288V14I | Intersil (Renesas Electronics America) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | TSSOP | Bulk | 2005 | e0 | 1 (Unlimited) | 14 | EAR99 | Tin/Lead (Sn/Pb) | 85°C | -40°C | 8542.39.00.01 | DUAL | 240 | 5V | 0.65mm | not_compliant | 30 | 14 | R-PDSO-G14 | 不合格 | 5.5V | 5V | INDUSTRIAL | 4.5V | 2-Wire, I2C, Serial | 31.3kB | TIMER, REAL TIME CLOCK | 0.032MHz | 1 | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 1/100SECOND | Y | YES | I2C | 1.2mm | 5mm | 4.4mm | Non-RoHS Compliant | 含铅 | |||||||||||||||||||||||||||||
![]() | X1288S16T1 | Intersil (Renesas Electronics America) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 表面贴装 | SOIC | 2005 | e0 | 1 (Unlimited) | 16 | EAR99 | Tin/Lead (Sn/Pb) | 70°C | 0°C | 8542.39.00.01 | DUAL | 240 | 5V | 1.27mm | 未说明 | 16 | R-PDSO-G16 | 不合格 | 5.5V | 5V | COMMERCIAL | 4.5V | 2-Wire, I2C, Serial | 31.3kB | TIMER, REAL TIME CLOCK | 0.032MHz | 1 | HH:MM:SS:hh (12/24 hr) | YY-MM-DD-dd | 1/100SECOND | Y | YES | I2C | 2.65mm | 10.3mm | 7.5mm | 符合RoHS标准 | 含铅 | |||||||||||||||||||||||||||||||
![]() | 1337DVGI | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 6 Weeks | 表面贴装 | TSSOP | 2006 | e3 | yes | 3 (168 Hours) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | 8542.39.00.01 | DUAL | 260 | 3.3V | 0.65mm | 30 | 8 | R-PDSO-G8 | 3.3V | 5.5V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | Y | I2C | 1.1mm | 3mm | 3mm | 无 | 符合RoHS标准 | |||||||||||||||||||||||||||||||||
![]() | 1337GDCGI | Integrated Device Technology (IDT) | 数据表 | 200 In Stock | - | 最小起订量: 1 最小包装量: 1 | Tin | 表面贴装 | SOIC | 8 | Bulk | 2006 | e3 | yes | Discontinued | 1 (Unlimited) | 8 | EAR99 | 85°C | -40°C | DUAL | 260 | 3.3V | 1.27mm | 30 | 8 | 3.3V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 5.5V | 1.8V | 8 | 0.4MHz | Clock | 1 | HH:MM:SS | YY-MM-DD-dd | SECONDS | Y | I2C | 1.75mm | 4.9mm | 3.9mm | 1.5mm | 无 | 符合RoHS标准 | 无铅 | ||||||||||||||||||||||||||||
![]() | 1338-31DCGI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 7 Weeks | 表面贴装 | SOIC | 8 | Tape & Reel | 2006 | e3 | yes | 活跃 | 1 (Unlimited) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | DUAL | 260 | 1.27mm | 30 | 8 | 3.3V | 3.6/5V | INDUSTRIAL | 5.5V | 2.45V | 0.032MHz | Clock | 1 | HH:MM:SS | SECONDS | N | NO | I2C | 1.75mm | 4.9mm | 3.9mm | 1.5mm | 无 | 符合RoHS标准 | 无铅 | ||||||||||||||||||||||||||||||
![]() | 1338-18DVGI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | 7 Weeks | 表面贴装 | MSOP | 8 | Tape & Reel | 2006 | e3 | yes | 活跃 | 3 (168 Hours) | 8 | EAR99 | Matte Tin (Sn) - annealed | 85°C | -40°C | DUAL | 260 | 3.3V | 0.65mm | 30 | 8 | 1.8V | 5.5V | 2/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 56B | 0.032MHz | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | N | NO | I2C | 970μm | 3mm | 3mm | 970μm | 无 | 符合RoHS标准 | 无铅 | |||||||||||||||||||||||||||
![]() | 1338C-31SRI8 | Integrated Device Technology (IDT) | 数据表 | N/A | - | 最小起订量: 1 最小包装量: 1 | Tin | 表面贴装 | SOIC | 16 | Tape & Reel | 2006 | e3 | no | Discontinued | 3 (168 Hours) | 16 | EAR99 | 85°C | -40°C | 8542.39.00.01 | DUAL | 260 | 1.27mm | 未说明 | 16 | 不合格 | 3.3V | 5.5V | 3.6/5V | INDUSTRIAL | 2-Wire, I2C, Serial | 56B | 0.032MHz | Clock | 1 | HH:MM:SS (12/24 hr) | YY-MM-DD-dd | SECONDS | N | NO | I2C | 2.65mm | 10.4mm | 7.6mm | 2.34mm | 符合RoHS标准 | 含铅 |
X1288S16T1
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
X1226V8IT2
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
ISL12021CVZ
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
X1286V14T1
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
X1288V14Z-2.7AT1
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
ISL12022MIBZ-T7A
Renesas Electronics America Inc.
分类:Clock/Timing - Real Time Clocks
MCP795B11T-I/ST
Microchip Technology
分类:Clock/Timing - Real Time Clocks
DS1672S-3 T
Maxim Integrated
分类:Clock/Timing - Real Time Clocks
1338C-31SRI
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1337DVGI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1339-31DCGI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1337GDVGI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1337GNLGI
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
ISL12027IVAZ
Intersil (Renesas Electronics America)
分类:Clock/Timing - Real Time Clocks
ISL12027IV30AZ-T
Intersil (Renesas Electronics America)
分类:Clock/Timing - Real Time Clocks
1337DCGI
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
PT7C4311WEX
Pericom Semiconductor Corp. (Diodes Incorporated)
分类:Clock/Timing - Real Time Clocks
X1288V14
Intersil (Renesas Electronics America)
分类:Clock/Timing - Real Time Clocks
X1288V14I
Intersil (Renesas Electronics America)
分类:Clock/Timing - Real Time Clocks
X1288S16T1
Intersil (Renesas Electronics America)
分类:Clock/Timing - Real Time Clocks
1337DVGI
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1337GDCGI
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1338-31DCGI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1338-18DVGI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
1338C-31SRI8
Integrated Device Technology (IDT)
分类:Clock/Timing - Real Time Clocks
