Abstract: There is disclosed a modular memory cell structure including a data latch, an occupancy bit latch and control logic. Each memory cell has access to the occupancy bit status of adjacent cells and to the input, output, control, and status busses. The occupancy status provides positional address information enabling each cell to determine if data in its data latch is the first, intermediate, or last element of a data queue. When a group of memory cells and an initialization circuit are interconnected, a modular integrated circuit design results which can function as either a first in-first out (FIFO) or a last in-first out (LIFO) memory.

Abstract: The telephone mounting apparatus comprises a rectangular frame base unit having a protrusion at one end and two slots at a second end for accepting either of two brackets. A telephone desk stand is constructed by inserting a first bracket into the slots in the base unit. The desk stand utilizes a first load bearing surface of the protrusion. A telephone wall mounting is constructed by inserting a second bracket into the slots in the base unit. The wall mounting utilizes a second load bearing surface of the protrusion.

Abstract: In the disclosed call transfer method and circuitry, audibly distinguishable ringing signals at a station set enable an answering party to determine whether a received call is either the original call or a previously answered call. Line status LEDs at each station set give specific visual indications to trace the progress of a call transfer.

Abstract: Small communication systems do not have a sufficiently large memory to store the vast amount of data required to determine the cost of interstate telephone calls using the conventional method. The disclosed telephone call cost establishing method and apparatus compresses the amount of data required by supplying a set of coordinates for a central point in each area code. The cost of an interstate call to any central office in an area code is then determined using the coordinates of the central point for that area code. Additionally, certain types of calls are priced using a predetermined price code stored in a variety of tables such as toll call allowed, frequently called numbers, personal line and facility tables.

Abstract: In the disclosed coded telephone ringing signal method and circuitry, audibly distinguishable ringing codes are generated by alternately shifting between at least a pair of single frequency tones at different modulation rates. Other distinguishable ringing codes are generated by changing both the modulation rates and tone frequencies utilized.

Abstract: A cartridge comprising circuitry and program instructions is added to a processor controlled telephone communication system to selectively change the operating system in accordance with the cartridge used.

Abstract: A memory write-enable circuit is disclosed which protects data stored in a random access memory (RAM) from erroneous write commands. The circuit is enabled, permitting write commands to RAM for a fixed time interval, only when two predetermined control signals occur within a prescribed time period. The circuit is disabled either by the elapse of the fixed time interval or by a clear signal.

Abstract: The method and apparatus encodes telephone ringing to identify both the origin and destination of a received call. The ring envelope of the ringing signal is divided into two segments. During the first segment, call origin information is encoded by varying the number of pulses or the pulse widths of a fixed frequency signal. Call destination information is encoded by time division multiplexing different frequencies into subsegments of the second segment.

Abstract: The flicker which results from large intensity differences in adjacent scan lines of a symbol displayed in an interlaced-field format is reduced by a non-linear signal filter and signal generator. The disclosed filter and signal generator changes the intensity of a scan line adjacent to a scan line of a symbol in response to a detected predetermined intensity difference between the adjacent scan line and the symbol scan line.