Output processing and output coupling circuit for a digital tone receiver

Abstract

A circuit is provided to convert a set of mutually exclusive digital signals representing presence or absence of individual tones of a Dual Tone Multiple Frequency (DTMF), or 2-of-8 signal, system into a four digit binary code word. Each different four bit word combination represents a different valid tone combination of the DTMF signal system. The four bit binary code word is represented by digits stored in an output register which serves as an output buffer. The loading of the output register is controlled by a single, multiple function signal which: (i) incorporates a coincidence timing function, (ii) provides a validity check which is also an integral part of the logical operation of the conversion, and (iii) causes the output signal to be interrupted upon a shift in input tones even though the shift in input tones may occur without interruption. The validity check which is also an integral part of the logical conversion further enables a construction which is readily modifiable after manufacture to accommodate different modes of use of a 2-of-8 signal system. The single, multiple function signal is further useful as an auxiliary output signal to aid in the processing of the four digit binary code word output signal, which takes place in the utilization circuit.