The AD664 is four complete 12-bit， voltage-output DACs on one monolithic IC chip. Each DAC has a double-buffered input latch structure and a data readback function. All DAC read and write operations occur through a single microprocessor-compatible I/O port. The I/O port accommodates 4-， 8- or 12-bit parallel words allowing simple interfacing with a wide variety of microprocessors. A reset to zero control pin is provided to allow a user to simultaneously reset all DAC outputs to zero， regardless of the contents of the input latch. Any one or all of the DACs may be placed in a transparent mode allowing immediate response by the outputs to the input data. The analog portion of the AD664 consists of four DAC cells， four output amplifiers， a control amplifier and switches. Each DAC cell is an inverting R-2R type. The output current from each DAC is switched to the on-board application resistors and output amplifier. The output range of each DAC cell is programmed through the digital I/O port and may be set to unipolar or bipolar range， with a gain of one or two times the reference voltage. All DACs are operated from a single external reference. The functional completeness of the AD664 results from the combination of Analog Devices’ BiMOS II process， laser-trimmed thin-film resistors and double-level metal interconnects.