Refresher:
Binary-coded decimal (BCD) is a class of binary encodings of decimal numbers.
Eg: 1001 in BCD representation represents decimal no. 9
1001 1001 in BCD representation represents decimal no. 99 and so on.
Doubt Clarification:
//Note: I/P is in BCD, Output is in Binary.
1 digit BCD input, binary output:
Max possible I/p: 1001 (9) O/P: = 1001 (9)
Input lines eqd. = 4
Output lines reqd. = 4
2 digit BCD input, binary output:
Max possible I/p: 1001 1001 (99) O/P: 1100011(99)
Input lines reqd. = 8 //count the no. of input bits
Output lines reqd. = 7 // ceil (log 99) = ceil (6.6293) = 7
//or simply count the no. of output bits
3 digit BCD input, binary output:
Max possible I/p: 1001 1001 1001 (999) O/P: 1111100111(999)
Input lines eqd. = 12
Output lines reqd. = 10 // ceil (log 999) = ceil (9.964) = 10
4 digit BCD input, binary output:
Max possible I/p: 1001 1001 1001 1001 (9999) O/P: 10011100001111(9999)
Input lines eqd. = 16
Output lines reqd. = 14 // ceil (log 9999) = ceil (13.28) = 14
Hence, Size of ROM with 16 input lines and 14 output lines is: 2^16 * 14 bits