Chapter 4 Software Development
pointer as necessary for string input.
If the character is a carriage return, the function echoes both it and a line feed back to the terminal emulator and stores the latter in memory instead.
The function repeats the above cycle the number of times specified by the count argument to the read() function. The compiler automatically determines this count from the standard I/O library function calling read().
The echo portions of the function are there to provide visual feedback when testing the firmware from the personal computer keyboard. If the user application program does not need this feedback, echoing can be dropped.
(2)write() function
Figure 4.5.4 gives a flowchart for function operation.
Read first character from string | ||
Character is line feed | Character is not line feed | |
Write carriage return to |
| |
transmit buffer | Write character to | |
| ||
| transmit buffer | |
Transmit character (CR) |
| |
in transmit buffer |
| |
Write character (LF) to |
| |
transmit buffer |
| |
Transmit character (LF) | Transmit character in | |
in transmit buffer | ||
transmit buffer | ||
| ||
Figure 4.5.4. write() Operation
The control flow is slightly more complicated than that for read(), but the entire operation can be described in a single sentence: The function reads a character from the buffer and transmits it, inserting a carriage return into the output stream before a line feed.
The function repeats the above cycle the number of times specified by the count argument to the write() function. The compiler automatically determines this count from the standard I/O library function calling write().
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