The CMX823 is a high performance, low power, audio tone decoder that can operate on low S/N signals. Each decoded tone frequency is user-defined to provide the flexibility to operate in a variety of paging, two-way radio and proprietary systems. Example systems and tones include: Motorola Quick Call series; GE groups A, B and Zetron, Reach and Plectron 2-tone radio paging; Motorola 5/6-tone paging; and the EIA, CCIR, ZVEI1 and EEA tonesets used for HSC radio paging and SELCALL. Up to 32 user-defined decode tone frequencies from 280Hz to 3500Hz are written to an internal RAM-based FIFO. (Two separate 32-tone FIFOs are provided and support fast switching between tone sets.) Each programmed tone (entry in the list) is user-assigned to one of two (or both) tone groups. 2-tone sequence decoding is simplified by dynamically enabling one or the other tone group via a mode selection. The CMX823 asserts an interrupt on tone decoding state transitions, e.g. notone to decoded tone, decoded tone to notone, etc. STATUS and DECODED TONE PARAMETERS Registers may then be read and indicate the decoder status, the target tone decoded and its tone group. The CMX823 operates over the -40C to +85C range and is available in 16-pin TSSOP (E4) and DIL (P3) packages.