The equipment you require is as follows:
There is no template document for this laboratory as you have seen what is required in the last two laboratories.
Please submit your laboratory write up to: http://moodle.dcu.ie/mod/assign/view.php?id=27689
Half Adders and Full Adders
7400: Quad 2-input NAND
7404: Hex Inverter
Construct the circuit as shown in Figure 1 using 7400 NAND Gates.
Figure 1: A 1-bit Half-adder circuit using NAND gates
Vary the inputs
B(i.e., 0 and +5V) to obtain all the possible combinations and complete a truth table for the sum output
Sand the carry output
C. You should wire up LEDs on your output for S and C to make this step more straightforward.
Comment in your report on whether this is as you expected.
Could we combine multiple half-adders to implement arbitrary width (n-bit) addition operations? Explain your answer in your logbook.
Build on your previous circuit to create the circuit as shown in Figure 2. Note: You may need to build this over two breadboards. Also, keep your wires colour coded correctly to make it easier to find faults in the circuit. There will be a lot of wires!
Figure 2: A 1-bit Full-Adder circuit using NAND gates
C(k-1)and complete a Truth table for the circuit.
C(k-1)represent? What does
What do you predict would be the outputs of the full-adder if the inputs were all left floating (i.e., not connected)? Test your prediction, and comment on the result.
The 4-bit Full Adder
A4) and (
B4) and a carry input (
C0). It generates the binary sum outputs (
S4 These are sigma on the chip) and the carry output (
C4) from the most significant bit. The carry input (C0) is there to allow you to connect two 4-bit adders together to create a 8-bit adder. For the moment, you can connect this input to GND. Be careful, it you leave it disconnected it will probably be received as a 1.
Figure 3: The 74HCT283 Four Bit Adder
Make sure that you know the order of your bits from MSB to LSB. So for the Sum outputs S4 should be your MSB and S1 should be your LSB - but also remember that A4 is your MSB and A0 is your LSB when you are inputting a value.
Consider the following 4-bit binary additions:
0110 + 0101
1011 + 0011
1110 + 0100
1111 + 1111
For each expression, predict what the sum bits and the carry-out bit should be, both for the case that the carry-in bit is
0 and that it is
1. Record your predictions in your write-up.
Now test all these predictions, using a 74HCT283. Record the results in your write-up. Comment on whether or not your predictions were satisfied.
- State briefly, but clearly, what you have learned from this session.
- What was the most difficult aspect of the lab?
- State one thing you enjoyed about the session.
- State one thing you disliked about the session.
- Add any final comment of your own.