August 30, 2010 W65C21 (W65C21N and W65C21S) Peripheral Interface Adapter (PIA) WDC reserves the right to make changes at any time without notice in order to improve design and supply the best possible product. Information contained herein is provided gratuitously and without liability, to any user. Reasonable efforts have been made to verify accuracy of the information but no guarantee whatsoever is given as to the accuracy or as to its applicability to particular uses. In every instance, it must be the responsibility of the user to determine the suitability of the products for each application. WDC products are not authorized for use as critical components in life support devices or systems. Nothing contained herein shall be construed as a recommendation to use any product in violation of existing patents or other rights of third parties. The sale of any WDC product is subject to all WDC Terms and Conditions of Sales and Sales Policies, copies of which are available upon request. Copyright (C) 1981-2010 by The Western Design Center, Inc. All rights reserved, including the right of reproduction in whole or in part in any form. 2 INTRODUCTION
The WDC W65C21 (W65C21N and W65C21S) is a very flexible Peripheral Interface Adapter (PIA) for use with WDC's 65xx, 68xx, and other 8-bit microprocessor families. The W65C21 provides programmed microprocessor control of up to two peripheral devices (Port A and Port B). Peripheral device control is accomplished through two 8-bit bidirectional I/O Ports, with individually designed Data Direction Registers. The Data Direction Registers provide selection of data flow direction (input or output) at each respective I/O Port. Data flow direction may be selected on a line-by-line basis with intermixed input and output lines within the same port. The "handshake" interrupt control feature is provided by four peripheral control lines. This capability provides enhances control over data transfer functions between the microprocessor and peripheral devices, as well as bidirectional data transfer between W65C21 Peripheral Interface Adapters in multiprocessor systems. FEATURES Low Power CMOS N-well silicon gate technology The W65C21N is plug replacement of NMOS and CMOS 6521 and 6821 devices with current limiting resistors The W65C21S is lower power, faster and direct drive outputs with no current limiting resistors. High speed/Low power replacement for Motorola/Rockwell/AMI/MOS Technology/MOSTEK/HITACHI/ ST Microelectronics/GTE/CMD 6520, 6521, 6820, 6821 PIA's Two 8-bit bidirectional I/O ports with individual data direction contro …
