Integrated Circuits

Integrated Circuit (IC) A silicon crystal (chip) containing electronic components that create the logic gates we’ve been looking at –SSI – Small Scale Integration –MSI – Medium Scale Integration –LSI – Large Scale Integration –VLSI – Very Large Scale Integration These refer to the number of logic gates contained on the chip

Technologies TTL – Transistor-Transistor Logic ECL – Emitter-Coupled Logic MOS – Metal-Oxide Semiconductor CMOS – Complementary Metal-Oxide Semiconductor These refer to the underlying characteristics of the process for turning silicon into gates

Digital Components Decoder Encoder Multiplexer Register Shift Register Counter Memory

Decoder Convert n input bits to a single output bit –For example: converting binary to octal (3-to-8) –What does the circuit look like? Start with a truth table Combinational Logic B0B0 B1B1 B2B2 Enable

Decoder Chaining Decoders can be chained Enable bit acts as the 4 th input bit We now have a 4-to- 16 decoder Combinational Logic B0B0 B1B1 B2B2 Enable Combinational Logic B0B0 B1B1 B2B2 Enable

Encoder Inverse of a decoder Convert one input bit to multiple output bits –For example: converting octal to binary (8- to-3) Combinational Logic B0B0 B1B1 B2B2 Enable

Multiplexer Routes one of 2 n input data lines to a single output line based on n selection lines How many inputs total? –How big is the truth table? Output Combinational Logic I0I0 I1I1 I2I2 I3I3 S0S0 S1S1 Inputs Selectors

Multiplexer 6 total inputs (4 data lines, 2 selector lines) leads to 2 6 = 64 rows of truth table! This is excessive and tedious More conveniently shown as thusly: Built from an n-to-2 n decoder with additional 2n input data lines SelectOutput S1S1 S0S0 Y 00I0I0 01I1I1 10I2I2 11I3I3

Multiplexer S0S0 S1S1 I3I3 I2I2 I1I1 I0I0 Output Not derived directly from the abridged truth table but from your knowledge of decoders

Register A multi-bit storage element made up of a group of flip-flops –Recall flip-flops store 1 bit each

Register CLR is a “clear” input for asynchronous initialization Data can be read out at any time Data is input with the clock signal, referred to as loading Loading can be further controlled through the use of additional combinational circuitry I3I3 I2I2 I1I1 I0I0 A3A3 A2A2 A1A1 A0A0 Clock Clear

Shift Register Like a “normal” register only bits can be shifted from one flip-flop to the next Serial Input Serial Output Clock

General Purpose Shift Register Bidirectional shifting (left and right) Serial input/output Parallel load Parallel output A multiplexer is provided to select the operation

General Purpose Shift Register Multiplexer operation selection Mode Control S1S1 S0S0 Operation 00No Change 01Shift Right 10Shift Left 11Parallel Load

General Purpose Shift Register What are they good for? –Integer multiplication by powers of 2 –Integer division by powers of 2 –Bit counting for parity –etc.

Counter A register that cycles though predetermined states based on an external input –We’ve seen these already –You should already know how to design one of these –Parallel load/clear functionality is often added via combinational circuitry

Memory A group of storage cells and associated access circuits Bits are grouped into words Words are the smallest addressable unit –Typically made up of 1 or more bytes (8- bits) Each word in memory is assigned a unique address

Memory 2 k word Memory n bytes/word Read Write Address Data In Data Out

Memory How many address lines? How many data input lines? How many data output lines? word Memory 2 bytes/word Read Write Address Data In Data Out

Memory K = “Kilo-bytes” = 2 10 bytes M = “Mega-bytes” = 2 20 bytes G = “Giga-bytes” = 2 30 bytes May be specified in either bytes or words Micro-processors will often talk of “Kilo- bits” or “Mega-bits” Be careful

Memory Read/Write Read –Apply binary address on the address lines –Apply a signal to the read input –Data is available on the data output lines Write –Apply binary address on the address lines –Apply binary data to the data input lines –Apply a signal to the write input

Memory Two types –RAM – Random Accessible Memory Operations we just looked at –ROM – Read Only Memory Has no input data lines Has no write input Has no read input (doesn’t need it – just acts when a valid address is supplied)

ROM Significantly cheaper than RAM since it lacks versatility How does the data get in there? –Mask programming – data is programmed in at the time of silicon fabrication –PROM – special programming devices allow the user to write data one time –EPROM – data is erased under ultra-violet light or electronically, but must be entirely erased and rewritten (can’t write single words)

To Do Read chapter 2, if you haven’t already Start reading chapter 4