| The thesis discusses the POS tax box, which is used in the tax department and it could intercept data, encrypt data, store data and transfer data. The article first discusses MODEM communication rule桯ayes Rule, AT Instruction Sets, Returned Code, S register and the hardware structure of MODEM. After comparing several plans, such plan is decided, that is, using one single MODEM and building some interface circuits to make up a typical MODEM, which is controlled by 8051 MCU. At the same time, some sub-models are designed detailedly. In order to let MODEM work correctly, some software are designed, such as initializing MODEM and sending AT instructions to MODEM. In addition, the communication protocol is decided in the article, and it is realized by using the 8051 assembly language and Visual Basic language. Finally, the thesis discusses some concepts of data encryption, giving some algorithm ideas.In order to finish the data checking, the POS tax box system communicates with PC of tax department through PSTN, it is connected with POS in the other hand. This project has been checked and accepted now. |
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