(Everyone who makes payments knows square. It is a great payment company. It was founded in 2009 and valued at $5 billion a few days ago. Mobile card swiping starts from square. Although there are many restrictions on the payment industry in China, there are still many "parties". With Chinese characteristics, such as the early music brush and box payment, including our card reader products, later lakala, UnionPay, etc. Instead of discussing his business model here, let's analyze how the card reader and mobile phone realize data communication.)