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Version history:
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2021-03-16	V1.00	AE TEAM
2022-07-17	V1.01	AE TEAM
1.适配ES-PDS-ES32F3696LX开发板

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Demo introduction:
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本示例功能：电池和市电同时供电的系统，市电供电时系统全速运行。LVD监测到市电掉电后(VDD<3.3V)
立即切换到电池供电，MCU也进入休眠状态，本例程STOP1与STOP2的唤醒端口为PF7。LVD
监测到市电恢复系统(VDD>3.5V)立即进入全速运行状态。

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测试环境:
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测试用板：
ES-PDS-ES32F3696LX-V1.0

辅助工具：
电流表 、可调电源

辅助软件：

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测试步骤：
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1) 编译工程，编译通过后通过ES-LinkII-OB将程序下载到目标芯片，断开USB线缆，将ES-LinkII-OB上的四位拨码开关拨到OFF档；
2) 将目标芯片电流测量点的IDD跳线帽断开，把电流表串接在ES-PDS-ES32F3696LX上的IDD电流测量点测试功耗；
3) 可调电源通过ES-PDS-ES32F3696LX的VDD和GND供电;
4) 按下ES-PDS板的RESET键;
5) 可调电源供电低于3.3V时，芯片进入低功耗状态。当给唤醒端口上升沿信号时，芯片唤醒再次进入休眠模式；
6) 可调电源供电高于3.5V时，测试用板全速运行。

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注意：
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1) 测试板与ESBridge需共GND。

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System clock:
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HRC 24MHz 6分频后PLL倍频到72MHz.

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Pin connection: 
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PMU_EXTI     ---- PF7[GPIO_FUNC_1]
PMU_STANDBY  ---- PA6[GPIO_FUNC_1]
LED          ---- PC12[GPIO_FUNC_1]
