I. (7.5 points) A common form for representing input data from a user is BCD
(binary coded decimal). Each group of 4
bits represents in binary the decimal digit (0 - 9). Design a 4-bit BCD adder.
The adder has two 4-bit BCD inputs, a carry-in bit; the outputs are a
4-bit BCD sum and a carry-out. Your
design should be limited to TTL-level parts (54/7400, 54/74x00 where x is LS,
S, ALS, AS,F, HCT, etc.). Use your BCD
adder in a 3 digit BCD and simulate the following operations:
(a)
023 + 039 (b) 154 + 348 (c) 751 + 149 (d)
897 + 998
You should attempt to use the fewest number
of ICs as possible. Determine a parts
list for your 3 digit BCD adder.
II. (7.5 points) Often times a BCD input must
be converted to ordinary binary for use in other parts of a digital
system. In this problem you will design
a converter for a 3 digit BCD number.
There are several possible alternatives, this problem will direct you
toward one of these alternatives. We
illustrate the idea with the following example:
To convert a 2 digit BCD number (e.g.
75), we write this as 75 =
7 x 10 + 5. Now, multiplication
by 10 can be done as follows: 7 x 10 =
7 x (8 + 2) = 7 x 8 + 7 x 2.
These are simple, since multiplication by 2k is just a left shift by k bits. Thus, 75 in BCD can be converted to binary
as follows:
5 + 7
x 2 +
7 x 8
Each addition here is a simple binary
addition. Think carefully about how
many bits are involved in each addition.
Extend this idea to convert any 3 digit BCD
number to binary. Use XC9500 series
CPLD in this project. Simulate the
following cases:
(a)
257 (b) 493 (c) 879
If you had to implement this design using MSI
parts, estimate the number of ICs that would have been required. If N
represents the number of BCD digits to be converted, estimate the increase in
logic needed as N goes from 3 to 4 to 5 to 6.
You may work in teams of two, with no
collaboration between teams. You should
turn in a printed schematic of each design, and the required simulations, and
parts list.
DUE: Tuesday, Nov 13, 2001