Optical transmission system for generating first-edge-based serial data

Abstract

Described herein is a system for transferring a binary data stream in a serial edge-based transmission format between a computer and a portable device such as the Timex.RTM. Data-Link.TM. watch. In the edge-based format expected by the Data-Link.TM. watch, individual data bits have first and second binary values which are represented by the presence or absence of signal edges at mark times which occur at a pre-selected bit rate. The system includes a computer having a digital output line which can be turned on and off by the computer at any time. The computer also has an internal timer which is programmed to generate timing signals at a frequency which is an integer multiple n of the pre-selected bit rate. An LED is operably connected to the digital output line so that the computer can switch the LED on and off at any time through the digital output line. An application program runs on the computer. The application program monitors the timing signals to transmit individual data bits of the binary data stream at corresponding n.sup.th timing signals. Specifically, the application program turns the LED on to create an optical signal edge at a particular n.sup.th timing signal if and only if the data bit corresponding to said particular n.sup.th timing signal has a `0` value. The application program then monitors the timing signals to turn the LED back off at an intermediate timing signal which occurs after said particular n.sup.th timing signal but before the next n.sup.th timing signal. The disclosed embodiment of the system includes a light wand having a distal end which is shaped to register against the face of the receiving watch. This aids the user in aligning the LED with the receiving sensor of the watch.