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The W65C21 Peripheral Interface Adapter (PIA), a flexible I/O device, has been used successfully with many different microprocessor families especially the 65xx, 68xx/68xxx and x86 microprocessors. Two program controlled 8–bit bi–directional (bit programmable) peripheral I/O ports allow direct interfacing between the microprocessor and selected peripheral units with manual or interrupt driven hand–shaking. The W65C21 is available in both CMOS and NMOS compatible versions.

Features of the W65C21

• 2 x 8−bit bidirectional I/O ports with individual data direction control
• Automatic “Handshake” control of data transfers
• 2 Interrupt outputs with program control
• Static to 14MHz operation, with high speed Port A, CA2 outputs
• 40 Pin Plastic Dip and 44 Pin Plastic PLCC versions
• 5V Power Supply
• Bus compatible with 14 MHz W65C02S and W65C816S
• Compatible with the 65xx and 68xx family of microprocessors
• Replacement for Motorola/Freescale / Rockwell / AMI / MOS Technology / MOSTEK / HITACHI / ST Microelectronics / GTE / CMD, 6520, 6521, 6820, 6821, PIA′s

W65C21N/W65C21S Differences

• The W65C21S is lower power, faster and direct drive outputs with no current limiting resistors on outputs ports and TTL input thresholds.
• The W65C21N is plug replacement of NMOS 6521 and 6821 devices with current limiting resistors on outputs ports and TTL input thresholds.
• The W65C21N Port A input buffers supply 200uA pull-up current at 2.4V in the input mode, while the W65C21S Port A input buffers supply 50uA pull-up current at 2.4V in the input mode.

Interface Signals Relationship

This part is a drop in replacement for many obsolete parts. WDC has compiled a list of cross part numbers and package types.