July 2008
Intermediate to advanced
544 pages
16h 52m
English
Content preview from Computers as Components, 2nd Edition
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96 CHAPTER 3 CPUs
Example 3.3 illustrates a combination of input and output.
Example 3.3
Copying characters from input to output using busy-wait I/O
We want to repeatedly read a character from the input device and write it to the output device.
First, we need to define the addresses for the device registers:
#define IN_DATA 0x1000
#define IN_STATUS 0x1001
#define OUT_DATA 0x1100
#define OUT_STATUS 0x1101
The input device sets its status register to 1 when a new character has been read; we must
set the status register back to 0 after the character has been read so that the device is ready
to read another character. When writing, we must set the output status ...
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