Techniques for interfacing a bar code scanner to a pc using a keyboard retransmit protocol

Abstract

A bar code scanner is equipped with a keyboard emulation mechanism so as to provide an enhanced interface to a keyboard controller port of a computing device such as a personal or laptop computer. The keyboard emulation mechanism eliminates the necessity of connecting an actual computer keyboard to the port by responding to the computing device's standard power-on diagnostic procedure as if it were effectively an electrical equivalent of a computer keyboard. The keyboard emulation mechanism can also be equipped to detect a keyboard inhibit signal at the keyboard controller port. If the keyboard emulation mechanism detects a keyboard inhibit signal while a data byte is being transmitted to the keyboard controller port, the keyboard emulation mechanism retransmits this data byte to the keyboard controller port. The data byte may specify a scan code corresponding to a keyboard key press or all or part of a decoded bar code. This retransmission process is repeated up to a specified number of times, so as to provide additional opportunities for the scan code to be inputted to the keyboard controller port if the port is momentarily disabled by the keyboard inhibit signal. For many applications, it is advantageous to repeat the retransmission process up to three times for a given data byte. If the data byte is still not successfully received after the third attempt, the process is no longer repeated.