Resumen en español

This article describes the characteristics of a modem sharing device. It is intented for RS232 enviroment, working with an half-duplex protocol, like poll-selet. It has 1 main port the modem (type DCE) and 4 sub-channels for terminals type DTE. This equipment was developed to satisfy the requeriments of a bank that needed to connet each of its offices spread along a city. Each office had an automatic teller machine, an customer terminal for balance request, and an small microcomputer network. All of this would be connet via only one modem. The sharing device was built around an Intel 87C51 microcontroller, because it has enough internal resources, low power consumption and need only a few external components for this purpouse.