SIM800C Couldn't pair with xxx because of an incorrect PIN or passkey

/*******************************************************************************
 *   SIM800C Couldn't pair with xxx because of an incorrect PIN or passkey
 * 说明：
 *     SIM800C蓝牙匹配不成功，设置为自动匹配蓝牙连接。
 * 
 *                                          2017-12-12 深圳 南山平山村 曾剑锋
 ******************************************************************************/

一、参考文档：
    1. SIM800 series Bluetooth AT commands
        http://www.raviyp.com/embedded/215-sim800-series-bluetooth-at-commands
    2. Bluetooth V2.1 SPP Terminal APK
        https://apkpure.com/bluetooth-v2-1-spp-terminal/com.ucconnect.ucbtadapter_hex

二、处理方法：
    1. SIM800 will be set to authenticate with Random PIN-code and when a pairing request comes in, it is automatically acknowledged by SIM800 and we need not do anything accept the pairing request
    2. AT+BTPAIRCFG=2
    3. AT+BTPAIRCFG?
    4. AT+BTPOWER=0
    5. AT+BTPOWER=1

三、测试
    1. AT+BTPOWER=1
    2. 打开Bluetooth SPP；
    3. 选择对应的蓝牙设备；
    4. 点击Connect；
    5. 看到+BTCONNECTING: "xxxxxxxxx","SPP"；
    6. AT+BTACPT=1
    7. 到这里就是连接OK了，可以发送数据了。