# CSC 371 - Systems I: Computer Organization and Architecture

## Dr. R. M. Siegfried

### Assignment 7 - p. 162-3/4-7a, 4-9, 4-10, 4-11

### Due Monday, November 28, 2011

### 4-7a

Design a combinational circuit that converts a 4-bit Gray code (Table 1-6
or in the Lecture #2) to 1 4-bit binary number. Implement the circuitwith exclusive-OR (XOR) gates.

### 4-9

ABCD-to-seven-segment decoder is a combinational circuit that converts a
decimal digit in BCD to an appropriate code for the selection of segments in
a display indicator used for displaying the decimal digit in a familiar form.
The seven outputs (a, b, c, d, e, f, g) select the corresponding segments in
the display as shown in the figure.The numeric display chosen to represent the
decimal digit is shown as well. Design the BCD-to-seven-segment decoder using
a minimal number of gates. The six invalid conbinations should result in a
blank display.

### 4-10

Design a 4-bit combinational circuit 2's complementer. (The output
generates the 2's complement of the input binary number.) Show that the
circuit can be constructed using exclusive-OR (XOR) gates. Can you predict
what the output functions are for a 5-bit 2=s complementer?

### 4-11

- Design a 4-bit combinational circuit incrementer. (A circuit that adds
one to a 4-bit binary number.) The circuit can be designed using four
half-adders.
- Design a 4-bit combinational circuit decrementer. (A circuit that
substracts one to a 4-bit binary number.) The circuit can be designed using
four half-adders.

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