The CSP1027 has a variety of significant programmable features not found in standard voice band codecs. The analog interface includes a microphone preamplifier with programmable gain settings, an output amplifier with gain programmable in 3 dB steps over a 45 dB range, and a regulated microphone power supply. An inactive mode allows a low-power standby state, and a mute function provides suppression of the analog output. On-chip antialiasing and anti-imaging filtering includes a selectable high-pass filter. The CSP1027 meets ITU-T G.712 voice band specifications. The programmable features of the CSP1027 are set by writing four on-chip control registers through the serial I/O interface. The codec's digital input/output uses a linear 16-bit two's complement data format that is also transferred through the serial I/O interface. The CSP1027 interfaces easily to the 16-bit serial ports of digital signal processors and other devices. The serial interface supports the Lucent fixed-point DSP family serial multiprocessor mode. This allows up to eight compatible devices, including two CSP1027s, to interface to each other on a common 4-wire bus using a time-division-multiplexing scheme.