Title: Combinational Circuit
1Combinational Circuit Arithmetic Circuit
- Parallel Adder
- Example 4-bit adder
2Combinational Circuit Arithmetic Circuit
- Usage Poling system (for 6 person)
- Use full adder and parallel adder 4-bit (binary)
- Each full adder can add 3 polls
3Combinational Gates Arithmetic Circuit
- Comparator
- Magnitude comparator compare two value A and B
to ensure if AgtB, AB or AltB - Classical method need 22n line in TT
- Explore dissimilarity
- How we compare two 4-bit value A(a3 a2 a1 a0) and
B(b3 b2 b1 b0) - If (a3gtb3) therefore AgtB
- If (a3ltb3) therefore AltB
- If (a3b3) therefore AB and so on..
4Combinational Gates Arithmetic Circuit
A3B3
x3
A3 B3
B3
A3B3 x3A2B2 x3x2A1B1 x3x2x1A0B0
A2
x2
B2
(AltB)
A1
x1
A3B3 x3A2B2 x3x2A1B1 x3x2x1A0B0
B1
A0
x0
(AgtB)
B0
(AB)
x3x2x1x0
5Combinational Circuit - Arithmetic Circuit
6Combinational Circuit MSI Circuit
- There are four useful MSI circuit
- Decoder
- Demultiplexer
- Encoder
- Multiplexer
- Block Diagram
7Combinational Circuit MSI Circuit
- DECODER
- Codes used for representing entity, e.g. your
name is a code which represent yourself (entity) - This code can be identified (or decoded) using a
decoder Provide code, identify entity - Change binary information from n input line
(maximum value for) 2n output line - Is known as line decoder n to m, or nm or nxm
decoder (mlt2n) - Might be used to generate 2n (or less) minterm
for n input variable
8Combinational Circuit MSI Circuit
- DECODER
- Example if code 00, 0, 10, 11is used to identify
four bulbs, therefore we need 2-bit decoder - This is 2x4 decoder which select output line
based on the given 2 bit. - Truth table
9Combinational Circuit MSI Circuit
- DECODER
- From the truth table, decoder circuit 2x4 is
- Notes each output in 2 variable minterm
expression (XY, XY, XY, XY)
10Combinational Circuit MSI Circuit
- DECODER
- Design of 3x8 decoder
- Usage? Conversion from binary to octal
11Combinational Circuit MSI Circuit
- DECODER
- In general for n-bit code, decoder suppose to
select up to 2n line
12Combinational Circuit MSI Circuit
- DECODER Function execution
- Example Full Adder
13Combinational Circuit MSI Circuit
- DECODER with Enable
- Most decoder has an enable signal, therefore it
only active when enable, E1 - Truth table
14Combinational Circuit MSI Circuit
- DECODER with Enable
- In MSI, enable signal for decoder is zero enable,
E, therefore this device only active when
enable E0
15Combinational Circuit MSI Circuit
- LARGE DECODER
- Large decoder can be built using small size
decoder - E.g. 38 decoder can be built using 24 (with 1
enable) as the following
16Combinational Circuit MSI Circuit
- LARGE DECODER
- E.g. 416 decoder can be built using two 38
decoder (with 1 enable) as the following. - How can you build 416 decoder by using 24
decoder with enable?
17Combinational Circuit MSI Circuit
- ENCODER
- Encoder is the inversion of decoder.
- Several sets of input line, select one, it
produce similar code for selected line - Consist of 2n (or less) input line and n output
line - Created from OR gate
- Example
18Combinational Circuit MSI Circuit