Ethernet Interface And Modem Interface Communication Design And Implementation Of The Expansion Board

With the technical development of Internet, more and more embedded equipments based on low cost microprocessor of 8-bit or 16-bit MCU , have begun to tend towards network.All these equipments inevitably faced a problem of how to connect with the bottom layer of Internet effectively in the course of building network.The Fiscal Cash Register(FCR) is a typical low-end embedded product based on 16-bit MCU ,which need to communicate with Internet .Now most FCR use IC card ,which has its own microprocessor,to save the information of declare data and invoice data at the FCR after security authentication. It need manual work to submit the IC card to department of revenue ,then to transmit data at the card to managing system of FCR. The disadvantage of this method is its inconvenience ,slowness and high cost of manpower and traffic.The widely use of Internet make it possible to transmit data through network at high speed.But we faced a question of how to connect with Internet effectively.There are three methods to choose.The first one is to add network interface on the main board of FCR.It is duty of FCR'S MCU to implement various protocols needed in the course of transmitting through Internet.However,it is very complicated to realize these protoclos . it will not only greatly increase the burden of MCU of FCR but also enhance the request of resources on the chip or out of the chip of MCU.In addition,it will influence the realization of normal function of FCR. The second choice is to add separate intelligent module on the main board .Transmitting protocols were completed by intelligent module.but this will add considerable cost of FCR.The user of FCR are very sensitive to the rise of price.It will bring disadvantageous impact on sale. The third choice is to connect with a communication equipment or a microcomputer.In this way,data will be transmitted to exterior facilities and then be transmitted to the remote by it.But such equipments usually cost very much and some even cost higher than FCR self.So it will be of practical value to design a special extended communication board ,which has characteristics of low cost,high stablization and will not occupy the resourses of system of FCR and not affect the reliability of normal function of FCR.Because FCR ususlly have a little data to transimt and require lower speed.Toreduce the cost of board ,the Data Communicating Board was designed to communicate using R1120 .16-bit Singlechip.to control RTL8019AS Ethernet Controller and 73M2901 MODEM interface chip.which can connect Internet both through telephone line and LAN.Using RS232 serial port ,The board can accurately exchange data with FCR by protocol defined by ourself. FCR can connect Internet by the board. Costs of hardware and software of the board will be greatly reduced by simplifying protocols of TCP/IP x PPP and so on .The simplified protocols such as PPP.Ethernet,TCP/IP,ICMRARP were written by R1120 assemble language,which is compatible with 80C186 MCU.In the end.we adopted separately MODEM module with 56k communication speed.This farther improved the speed and stablization of communication through telephone line to Internet.In the system of Fiscal Cash Register Data Transfered Through Internet.the communication board took on some duty of FCR and acted as a client terminal to connect with remote server.The board acted as one of a crucial part in the item of 'Declare System Through Internet of Ficial Cash Register'.It was identified by committee of Technology Bureau of ShanDong Province.Experiments prove that The board has characteristic of high efficiency.stabilization and cheapness .At presentthe board was used in Commercial Co.Langchao Group.lt worked stably and transmitted data exactly.