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按键扫描 51单片机加8279
8279通过74LS 138译码器扩展4×4键盘、6位显示器。
由3-8译码器对SL0～SL2译出键扫描线，由另一3-8译码器译出显示器的位扫描线，并采用了编码扫描方式。
为了防止出现重键现象，扫描输出线高位SL3不参加键扫描译码。CPU对8279的监视采用了查询方式，故8279的中断请求信号IRQ悬空未用。
-Scan button 82,798,279 plus 51 single-chip decoder 74LS 138 through the expansion of 4 × 4 keyboard, the display 6. From 3-8 decoder SL0 ~ SL2 translated to the key scanning line, by another 3-8 decoder translated display scan line, and uses code scanning. In order to prevent the emergence of the phenomenon of re-key, scan the output line does not take part in high level SL3 scan decoding keys. CPU on the 8279 surveillance using the query mode, the 8279 interrupt request signal IRQ left unused.
