第2章_F2812结构与最小系统(13)

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DSP控制器原理及应用

扩展存储器的最小系统需要的控制总线CB思考题2-8:无外设占用总线请求时,该 XHOLD(外设占用请求,输入)引脚设应何处理? External Hold Request. XHOLD, when active (low), requests the XINTF to release the external bus and place all buses and strobes into a high-impedance state. The XINTF will release the bus when any current access is complete and there are no pending accesses on the XINTF. 25

DSP控制器原理及应用

扩展存储器的最小系统需要的控制总线CBXHOLDA(外设占用应答,输出) External Hold Acknowledge. XHOLDA is driven active (low) when the XINTF has granted a XHOLD request. All XINTF buses and strobe signals will be in a high-impedance state. XHOLDA is released when the XHOLD signal is released. External devices should only drive the external bus when XHOLDA is active (low).

思考题2-9:无外设占用总线请求时,该引脚设应何处理?

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