ELEC 2220 - Computer Systems
Homework #14
Due: Friday, 10-3-08
1. Six ASCII characters, representing six decimal digits entered from a keyboard, are stored beginning at data
address STRG. Write a program to convert this string of characters to a packed BCD number and store it at
data address PACK. (A program would need to do this when numbers are entered from a keyboard.)
For example, if you type the number 135876 on the keyboard, the characters would be stored in memory as
follows: STRG => '1' (31h) - Most significant digit (100000’s)
STRG+1 => '3' (33h) – Next most significant digit (10000’s)
STRG+2 => '5' (35h) – Next most significant digit (1000’s)
STRG+3 => '8' (38h) - Next most significant digit (100’s)
STRG+4 => '7' (37h) – Next most significant digit (10’s)
STRG+5 => '6' (36h) - Least significant digit (1’s)
Your program is to convert this to packed BCD format. The above would be stored in memory (most
significant byte first) as follows:
PACK => 13h
PACK+1 => 58h
PACK+2 => 76h
Demonstrate your program in CodeWarrior by initializing the six bytes of STRG as shown above, and the
three bytes of PACK to 00. Print the debug window showing the final values of these memory locations after
executing the program. (You might also want to test your program on additional sets of data.)
2. Write a program to do the inverse of the above operation, i.e. given the three-byte packed BCD number
starting at PACK, “unpack” and convert it to a string of six ASCII characters, representing the digits, storing
them in array STRG.
Demonstrate your program in CodeWarrior by initializing the six bytes of STRG to 00, and the three bytes of
PACK to the values shown above. Print the debug window showing the final values of these memory
locations after executing the program.