The NTE6821 is a peripheral interface adapter (PIA) in a 40–Lead DIP type package capable of interfacing the Microprocessing Unit (MPU) to peripherals through two 8–Bit bidirectional peripheral data buses and four control lines. No external logic is required for interfacing to most peripheral devices.
The functional configuration of the PIA is programmed by the MPU during system initialization. Each of the peripheral data lines can be programmed to act as an input or output, and each of the four control/interrupt lines may be programmed for one of several control modes. This allows a high degree of flexibility in the over–all operation of the interface.
 
Full spec sheet:
https://www.nteinc.com/specs/6800to6899/pdf/nte6821.pdf