14 lines
716 B
Markdown
14 lines
716 B
Markdown
Apple II Dual-6522 GPIO Card
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This is a fairly straightforward implementation of a GPIO interface for the
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Apple II, based on a pair of 6522 VIAs. It is an extension of a design
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published in c't Magazine in 1985, with the control lines on each 6522 also
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brought out to header pins, the data bus buffered with a 74LS245, and the
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ɸ2 signal needed by the 6522s generated by a pair of flip-flops in a 74LS74
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in accordance with a technote published by Apple on the subject. Most
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components are surface-mount to reduce needed board area, though the 6522s
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were kept in DIP form to allow use of either NOS (new old stock) 6522s from
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whatever suppliers or the currently available WDC W65C22S.
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