Marker Code Method for Keyboard Scan Codes
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
This article describes the use of special marker code signals for distinguishing new keys on the Ferrari keyboard to application software written specifically for that keyboard while retaining compatibility for software written for previous keyboards. The marker codes are ignored by the latter software. The personal computer (PC) keyboard uses scan codes to tell the system which keys have been pressed and released. When a key is pressed, a code is sent to the system representing that key, and when released, another code is sent, representing the release of that key. An example is shown in Fig. 1. The up-arrow/numeral-8 key is the only key on the keyboard with that particular function, so when its scan code is received, the system knows exactly how to translate it. A single scan code is all that is necessary.