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AN-006: W65C21S Replacement Notes for Obsolete PIA Devices

The W65C21S can replace older and obsolete NMOS and CMOS versions of the 6520/6521/6820/6821 Peripheral Interface Adapter (PIA) supplied by WDC's licensees and others.

Comparison of W65C21S to other PIA Devices

The W65C21S is Pin and Functionally Compatible with the following devices.

CMD / GTE - G65SC21
Hitachi - HD6821, HD6321 (CMOS)
MOS Technology - 6521
Motorola / Freescale - M6820, M6821
Rockwell - R6520, R6521, R65C21
ST Micro - EF6821

Features for New Designs

- RoHS/Green Compliant
- Two 8-bit bidirectional I/O Ports with individual data direction control
- Static to 14MHz operation
- The PIA has been used with many different 8/16/32-bit processors
- Two program controlled interrupt outputs
- Extensible architecture provides easy I/O expansion
- Compatible with the WDC 65xx 14MHz microprocessor family 8-bit data bus

Buffer Differences

- Port A Input buffers supply 50 uA pull up current
- Port A Output buffers match Port B drive current when in output mode
- The changes were made to both reduce the current for lower power CMOS systems and to speed up the output drivers for higher speed

PDIP and PLCC Pin Configuration of the W65C21S

W65C21S 40 pin PDIP     W65C21S 44 pin PLCC
W65C21S 40 pin PDIP     W65C21S 44 pin PLCC


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2166 E. Brown Rd. Mesa, Arizona 85213
phone: 480 962-4545, fax: 480 835-6442

Last updated 01/05/2021
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