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6.异步通信接口适配器上节中我们讨论了MPU通过PIA与外设进行通信,数据的接收与送出都是8位同时并行传送。因此PIA外设之间的数据线需每侧8条。在远距离数据通信中,采用8条或16条数据线从PIA连到远方装置便不合适了。异步通信接口适配器(ACIA)允许采用一根线以串行格式传送数据,而不是PIA所需要的每侧8根线。ACIA能够起到把串行转换为并行或并行转换为串行的作用(图22)。
6. Asynchronous Communication Interface Adapter In the previous section, we discussed the MPU through PIA and peripherals to communicate, receive and send data are 8-bit simultaneous transmission. Therefore, PIA peripherals between the data lines to be 8 per side. In long-distance data communications, the use of 8 or 16 data lines from the PIA to distant devices would not be appropriate. Asynchronous Communication Interface Adapter (ACIA) allows data to be transmitted in a serial format using one line instead of the eight lines on each side required by the PIA. ACIA can play the role of converting serial to parallel or parallel to serial (Figure 22).