TAILIEUCHUNG - HandBooks Professional Java-C-Scrip-SQL part 190

Tham khảo tài liệu 'handbooks professional java-c-scrip-sql part 190', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | I O Map If a separate I O space is present it will be necessary to repeat the memory map exercise to create an I O map for the board as well. The process is exactly the same. Simply create a table of peripheral names and address ranges organized in such a way that the lowest addresses are at the bottom. Typically a large percentage of the I O space will be unused because most of the peripherals located there will have only a handful of registers. The I O map for the Arcom board is shown in Figure 5-3. It includes three devices the peripheral control block PCB parallel port and debugger port. The PCB is a set of registers within the 80188EB that are used to control the on-chip peripherals. The chips that control the parallel port and debugger port reside outside of the processor. These ports are used to communicate with the printer and a host-based debugger respectively. Figure 5-3. I O map for the Arcom board The I O map is also useful when creating the header file for your board. Each region of the I O space maps directly to a constant called the base address. The translation of the above I O map into a set of constants can be found in the following listing I O Map Base Address Description _ 0000h Unused FC00h Source VIEW Debugger Port SVIEW FD00h Parallel I O Port PIO FE00h Unused FF00h Peripheral Control Block PCB define SVIEW_BASE OxFCOO define PIO_BASE OxFDOO define PCB BASE OxFFOO Learn How to Communicate Now that you know the names and addresses of the memory and peripherals attached to the processor it is time to learn how to communicate with the latter. There are two basic communication techniques polling and interrupts. In either case the processor usually issues some sort of commands to the device by way of the memory or I O space and waits for the device to complete the assigned task. For example the processor might ask a timer to count down from 1OOO to O. Once the countdown begins the processor is

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