Combinational Circuit Arithmetic Circuit Parallel Adder Example 4
Combinational Circuit – Arithmetic Circuit • Parallel Adder Example: 4 -bit adder MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 1
Combinational 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 MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 2
Combinational Gates – Arithmetic Circuit • Comparator – Magnitude comparator: compare two value A and B to ensure if A>B, A=B or A<B – Classical method need 22 n line in TT – Explore dissimilarity – How we compare two 4 -bit value A(a 3 a 2 a 1 a 0) and B(b 3 b 2 b 1 b 0) – If (a 3>b 3) therefore A>B – If (a 3<b 3) therefore A<B – If (a 3=b 3) therefore A=B and so on. . MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 3
Combinational Gates – Arithmetic Circuit A 3’B 3 x 3 B 3 A 2 A 3 B 3 ’ x 2 B 2 A 1 x 1 B 1 A 0 x 0 B 0 A 3’B 3 + x 3 A 2’B 2 + x 3 x 2 A 1’B 1 + x 3 x 2 x 1 A 0’B 0 (A<B) A 3 B 3 ’ + x 3 A 2 B 2 ’ + x 3 x 2 A 1 B 1’ + x 3 x 2 x 1 A 0 B 0’ (A>B) (A=B) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR x 3 x 2 x 1 x 0 4
Combinational Circuit - Arithmetic Circuit • Comparator MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 5
Combinational Circuit – MSI Circuit • There are four useful MSI circuit – – Decoder Demultiplexer Encoder Multiplexer • Block Diagram MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 6
Combinational 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) 2 n output line • Is known as line decoder n to m, or n: m or nxm decoder (m<=2 n) • Might be used to generate 2 n (or less) minterm for n input variable MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 7
Combinational Circuit – MSI Circuit DECODER • Example: if code 00, 0, 11 is used to identify four bulbs, therefore we need 2 -bit decoder • This is 2 x 4 decoder which select output line based on the given 2 bit. • Truth table MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 8
Combinational Circuit – MSI Circuit DECODER • From the truth table, decoder circuit 2 x 4 is • Notes: each output in 2 variable minterm expression (X’Y’, X’Y, XY’, XY) MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 9
Combinational Circuit – MSI Circuit DECODER • Design of 3 x 8 decoder • Usage? Conversion from binary to octal MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 10
Combinational Circuit – MSI Circuit DECODER • In general: for n-bit code, decoder suppose to select up to 2 n line MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 11
Combinational Circuit – MSI Circuit DECODER – Function execution • Example: Full Adder MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 12
Combinational Circuit – MSI Circuit DECODER with Enable • Most decoder has an enable signal, therefore it only active when enable, E=1 • Truth table MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 13
Combinational Circuit – MSI Circuit DECODER with Enable • In MSI, enable signal for decoder is zero enable, E’, therefore this device only active when enable E’=0 MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 14
Combinational Circuit – MSI Circuit LARGE DECODER • Large decoder can be built using small size decoder • E. g. 3: 8 decoder can be built using 2: 4 (with 1 enable) as the following MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 15
Combinational Circuit – MSI Circuit LARGE DECODER • E. g. 4: 16 decoder can be built using two 3: 8 decoder (with 1 enable) as the following. • How can you build 4: 16 decoder by using 2: 4 decoder with enable? MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 16
Combinational 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 2 n (or less) input line and n output line • Created from OR gate • Example: MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 17
Combinational Circuit – MSI Circuit Truth table MOHD. YAMANI IDRIS/ NOORZAILY MOHAMED NOOR 18
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