Abstract: The present invention is a magnetic tape-based "voice mail" multi-user message system. The system transmits audio prompts to callers to help guide them through the various procedures. The callers respond with Touch-Tone commands. A novel circuit is provided to detect these tone commands without significant interference from the audio prompt signals. This circuit is highly insensitive to deviations in the impedance of the incoming telephone line from its expected value. A circuit is also provided to prevent Touch-Tone commands which are recorded on tape from being re-executed when they are played back from the tape. A single L.E.D. indicator on each recipient's telephone set indicates the status of the system: idle with new message waiting; idle without new message waiting; busy with new message waiting; or busy without new message waiting.

Abstract: An electrical circuit is described that requires a reduced number of data bits for character-address and video-mode information by using a predetermined bit combination of the video-mode information as part of the character-address information. Character-address and video-mode information is output from a random access memory (RAM) to a character read only memory (ROM) and a video-mode detection circuit that produces outputs to enable video-mode circuits in the video control circuitry. One output of the video-mode detection circuit is coupled to an address input of the character ROM that has characters divided into two character sets. A predetermined bit combination of the video-mode information produces an output from the video-mode detection circuit that selects one of the character sets while the other bit combinations produce an output from the detection circuit that selects the other character set.

Abstract: Disclosed herein is an apparatus for displaying a logic waveform on a raster scan display device such as a CRT. A part of an input logic signal is delayed for forming a former bit, and the input logic signal acts as a present bit. A memory device stores a special pattern determined in accordance with results of logic operation of the present and former bits. An image dot of the pattern is addressed by the present and former bits and raster line position (number) information, and the output therefrom is applied as an intensity control signal to the display device. Since the memory device does not need FONT information, this invention needs very little software manipulation of data, and the capacity of the memory device is small. In addition, this invention can display glitches and graticule tick marks.