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

二、处理方法：
    . 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
    . AT+BTPAIRCFG=
    . AT+BTPAIRCFG?
    . AT+BTPOWER=
    . AT+BTPOWER=

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