当CE=0，IO/M=0时，8155只能做片外RAM使用，共256 B。其寻址范围由以及AD0～AD7的接法决定，这和前面讲到的片外RAM扩展时讨论的完全相同。当系统同时扩展片外RAM芯片时，要注意二者的统一编址。对这256 B RAM的操作使用片外RAM的读/写指令“MOVX”。



作扩展I/O用

当 CE=0，IO/M=1时，此时可以对8155片内3个I/O端口以及命令/状态寄存器和定时/计数器进行操作。与I/O端口和计数器使用有关的内部寄存器共有6个，需要三位地址来区分。-When CE = 0, IO/M = 0, the 8155 can only do chip RAM to use, a total of 256 B. The address range from well AD0 ~ AD7 the connection decision, which referred to the previous extended-chip RAM to discuss the same. When the system while expanding off-chip RAM chips, both should pay attention to the unity of addressing. The operation of this 256 B RAM chip RAM using read/write instruction " MOVX" . Expanding the I/O available when CE = 0, IO/M = 1, the point can be within the three 8155 I/O ports, and command/status registers, and timer/counter operation. And I/O ports and the use of the internal counter register a total of 6, you need to distinguish between the three addresses.