使用VC++编写，实现Modem的AT指令的操作，包括串口初始化，拨号、挂断，读写数据等

这是一个封装好的发送AT指令modem程序，通过串口读写操作，发送AT指令实现拨号上网功能-This is a good package to send AT command modem program, read and write operations through the serial port and send AT commands to achieve dial-up Internet access