因此,微处理器本身不能做任何事情,它需要与内存,额外的外围设备或IO设备链接。此链接称为接口。
8085中的I / O设备的接口可以通过两种方式完成:
1.内存映射的I / O接口:
在这种接口中,我们分配一个内存地址,该地址的使用方式与使用普通内存位置的方式相同。
2. I / O映射的I / O接口:
一种接口,其中我们将8位地址值分配给可以使用IN和OUT指令访问的输入/输出设备,称为I / O映射I / O接口。
内存映射的I / O接口和I / O映射的I / O接口之间的区别:
Features | Memory Mapped IO | IO Mapped IO |
---|---|---|
Addressing | IO devices are accessed like any other memory location. | They cannot be accessed like any other memory location. |
Address Size | They are assigned with 16-bit address values. | They are assigned with 8-bit address values. |
Instructions Used | The instruction used are LDA and STA, etc. | The instruction used are IN and OUT. |
Cycles | Cycles involved during operation are Memory Read, Memory Write. | Cycles involved during operation are IO read and IO writes in the case of IO Mapped IO. |
Registers Communicating | Any register can communicate with the IO device in case of Memory Mapped IO. | Only Accumulator can communicate with IO devices in case of IO Mapped IO. |
Space Involved | 216 IO ports are possible to be used for interfacing in case of Memory Mapped IO. | Only 256 I/O ports are available for interfacing in case of IO Mapped IO. |
IO/M` signal | During writing or read cycles (IO/M` = 0 ) in case of Memory Mapped IO. | During writing or read cycles (IO/M` = 1) in case of IO Mapped IO. |
Control Signal | No separate control signal required since we have unified memory space in the case of Memory Mapped IO. | Special control signals are used in the case of IO Mapped IO. |
Arithmetic and Logical operations | Arithmetic and logical operations are performed directly on the data in the case of Memory Mapped IO. | Arithmetic and logical operations cannot be performed directly on the data in the case of IO Mapped IO. |