GENERAL DESCRIPTION
The ALD521D is a digital controller designed to interface to the ALD500 or ALD500R integrating dual slope analog processors as a chip set for building a precision analog-to-digital converter. With the ALD521D and ALD500R, together with a few external capacitors and resistors, a precision Analog to Digital converter with auto zero and auto-polarity can be implemented.

FEATURES AND BENEFITS
• Low cost, simple functionality
• PC parallel printer port interface standard
• Support resolution up to 23 binary bits + sign polarity bit
• Easy to use to acquire up to 23 bit linearity and noise performance
• Integration time can be set by the user
• Easy user evaluation and setting of conversion parameters
• Low power dissipation - 4 mA typical including crystal oscillator
• On-chip Crystal Oscillator Circuit
• Two way asynchronous handshake data transfer
• Conversion speed versus resolution trade-off
• Power down (sleep mode) control input to power down to 2 µA
• Chip Select control input
• High impedance DV, DOUTand SCLK when chip not selected
• Single 3 V to 5 V power supply

APPLICATIONS
• Operate in conjunction with ALD500/ALD500R Precision analog signal processors
• High accuracy DC voltage measurement functions
• Portable battery operated instruments
• PC-based software control or stand-alone operation (without other processors or PC)
• Serial digital output interface to other microprocessors or  microcontrollers