1. ACOE161 (Spring2007)MSI Devices1 Revision on MSI Devices M. Mano & C. Kime: Logic and Computer Design Fundamentals (Chapter 5)

2. ACOE161 (Spring2007)MSI Devices2 Medium Scale Integration (MSI) devices are digital devices that are build using a few tens to hundreds of logic gates. MSI devices are used as discrete devices packed in a single Integrated Circuit (IC), or as building blocks for other, more complex devices such as memory devices or microprocessors. Some typical MSI devices are the following: –Encoders and Decoders –Multiplexers and Demultiplexers –Full Adders –Latches and flip flops –Registers and Counters

3. ACOE161 (Spring2007)MSI Devices3 Examples of MSI Devices Decimal to BCD Encoder BCD to Decimal Decoder 4-to-1 Multiplexer

4. ACOE161 (Spring2007)MSI Devices4 Decoders A decoder is a combinational digital circuit with a number of inputs ‘n’ and a number of outputs ‘m’, where m= 2 n Only one of the outputs is enabled at a time. The output enabled is the one specified by the binary number formed at the inputs of the decoder. On the circuit below, the inputs of the decoder are connected on three switches, forming the number 5 [(101) 2 ], thus only the lamp #5 will be ON

5. ACOE161 (Spring2007)MSI Devices5 2 to 4 Line Decoder:

6. ACOE161 (Spring2007)MSI Devices6 3 to 8 Line Decoder:

7. ACOE161 (Spring2007)MSI Devices7 3 to 8 Line Decoder: (Implementation using two 2-to-4 decoders)

8. ACOE161 (Spring2007)MSI Devices8 3 to 8 Line Decoder: (Implementation using two 2-to-4 decoders)

9. ACOE161 (Spring2007)MSI Devices9 4 to 16 Line Decoder: (Implementation using four 2-to-4 decoders)

10. ACOE161 (Spring2007)MSI Devices10 ENCODERS A decoder in general is a combinational digital circuit with with a number of inputs ‘m’ and a number of outputs ‘n’, where n = log 2 m A binary encoder has precisely the opposite functionality of the binary decoder. A priority encoder is a special case of encoder used in computer interrupt mechanisms to specify which device requests service and prioritize interrupts that occur at the same time EI3I2I1I0A1A0

11. ACOE161 (Spring2007)MSI Devices11 Multiplexers A multiplexer is a device that has a number of data inputs “m”, and number of control inputs “n” and one output, such that m=2 n. The output has always the same value as the data input specified by the binary number at the control inputs. The rotary switch (selector) shown in figure (a) below, is equivalent to a 4-to-1 multiplexer. The sliding switch shown in figure (b) below, is equivalent to an 8-to-1 multiplexer.

12. ACOE161 (Spring2007)MSI Devices12 Internal structure of a 2-to-1 multiplexer. The design of a 2-to-1 multiplexer is shown below. If S=0 then the output “Y” has the same value as the input “ I 0 ” If S=1 then the output “Y” has the same value as the input “ I 1”

13. ACOE161 (Spring2007)MSI Devices13 1-bit Full Adder

14. ACOE161 (Spring2007)MSI Devices14 4-bit Full Adder To obtain a 4-bit full adder we cascade four 1-bit full adders, by connecting the Carry Out bit of bit column M to the Carry In of the bit column M+1, as shown below. The Carry In of the Least Significant column is set to zero. Example: Find the bit values of the outputs {Cout,S3..S0} of the full adder shown below, if {A3..A0 = 1011} and {B3..B0 = 0111}.