Point-Of-Sale Terminals With Loop Trace Function
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
This article describes a technique and apparatus whereby an ordinary point-of-sale terminal can be used as a test equipment terminal for observing data on the communications loop. The figure shows a communications network wherein a plurality of terminals are coupled to a store controller by the loop communications medium. A well-known SDLC (synchronous data link control) protocol is used to transmit messages between the terminal and the controller. All messages placed on the data loop by the controller or a terminal are preceded by an address. Under normal operating conditions each terminal on the loop is given a unique loop address or addresses. This address is used to identify messages from the terminal to the store controller, or vice versa.