Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 361

L7.3 Keypad input. Use the circuit shown in Figure 7.7 to perform keypad input practice. The
procedure is as follows:
Step 1
Configure the upper four pins of Port P3 for output and the lower four pins of P3 for input.
Step 2
Initialize the LCD properly.
Step 3
Output the message “Enter an integer:” on the first row of the LCD. After seeing this
message, you enter a number on the keypad. Use the F key (or other key) to terminate
the number. Your program reads in the number, converts it into a binary, and saves it in a
buffer.
Step 4
Output the message “Enter another integer:” on the first row of the LCD. After seeing this
message, you enter a number on the keypad. Use the F key to terminate the number. Your
program reads in the number, converts it into a binary, and saves it in a buffer.
Step 5
Compute the gcd of these two numbers and display it on the LCD screen as follows:
The gcd of xxxx and
yyyy is zzzz.
where xxxx and yyyy are the numbers that you entered from the keypad and zzzz
is the gcd of these two numbers.