1) An arithmetic logic unit (ALU) is a digital circuit capable ofperfonning both
arithmetic and logic operations.
2)The term multiplex means "many into one."
3)The opposite of multiplex is demultiplex, which means "one into many.
4)Taking digital information from the output of a computer and changing it into
another form is accomplished
with a decoder,
5)A microcomputer designed to control a given machine, process, or system
6)The central processing unit (CPU) is the brain of a digital computer. It is
constructed using an ALU along with a number of registers and counters.
7)A digital signal refined to as the system clock is used as a reference to time
when specific operations take place. The clock signal is usually a periodic,
rectangular waveform
8)The CPU is capable of computation and decision, but it must have specific
instructions telling it exactly what to do and when to do it. This set of instructions
is called a program. A program is a detailed list of operations written by a human
programmer
9)A direct memory access (DMA) block is generally included to alleviate this
problem. As seen in Fig. 1.31 b, the DMA allows information to move directly
from an input device into memory, or from memory directly to an output device.
While information is being transfened via the DMA, the CPU is free to cany on its
computational or logical operations. This greatly improves system efficiency as
well as speed of operation.
10) ICs are categorized by size according to the number of gates contained on
each chip. There is no absolute rule, but an IC having fewer than 10 or 12 gates
is usually referred to as a small-scale integration (SSI) IC.
11) If there are more than 100 gates but fewer than 1000, the IC is called a
large-scale integration (LSI) JC. An IC having more than 1000 gates is referred to
as a very large-scale integration (VLSI) JC. A large complex system such as
semiconductor memory or a microprocessor will be either LSI or VLSI.
12) ICs are further categorized according to the type of transistors used. The two
basic transistor types are bipolar and metal-oxide-semiconductor (MOS). Bipolar
technology is faster but requires more power, and is generally preferred for SSI
and MSI. MOS is slower, but requires much less power and also occupies a much
smaller chip area for a given function. MOS is therefore preferred for LSI and is
widely used in applications such as pocket calculators, wristwatches, hearing
aids, and so on
13) Emitter-Coupled Logic Emitter-coupled logic (ECL) is considerably faster than
any of the TTL families, but the power required for each gate is also much higher
14) CMOS has better noise margin characteristics over TTL
15) flip-flop is An electronic circuit that can store one bit of a binary number.
16) logic circuit is A digital circuit, a switching circuit, or any kind of two0 state
circuit that duplicates mental processes.
17) parallel shifting is Transferring all bits in a binary number (digital data)
simultaneously.
18) serial shifting is Transferring each bit in a binary number (digital data), one
bit at a time, one after the other.
19) Multiplex means many into one. A multiplexer is a circuit with many inputs
but only one output. By applying control signals, we can steer any input to the
output. Thus it is also called a data selector and control inputs are termed select
inputs
20) a low strobe enables the multiplexer, whereas a high strobe disables the
multiplexer
21) the multiplexer is active (enabled) when the STROBE is low and inactive
(disabled) when it is high. Because of this, the STROBE is called an active-low
signal; it causes something to happen when it is low rather than when it is high
22) Demultiplex means one into many. A demultiplexer is a logic circuit with one
input and many outputs. By applying control signals, we can steer the input
signal to one of the output lines
23) A decoder is similar to a demultiplexer, with one exception-there is no data
input
24) Exclusive-OR gates are ideal for checking the parity of a binary number
because they produce an output 1 when the input has an odd number of 1 s.
Therefore, an even-parity input to an exclusive-OR gate produces a low output,
while an odd-parity input produces a high output.
25) A read-only mem01y (which is abbreviated ROM and rhymes with Mom) is an
IC that can store thousands of binary numbers representing computer
instructions and other fixed data
26) PALs are chips that. Are programmable arrays of logic. Unlike the PROM with
its fixed AND array and programmable OR array, a PAL has programmable AND
array and a fixed OR array. The PAL has the advantage of having up to 16 inputs
in commercially available devices.
27) PLA A programmable logic array.
PLD A programmable logic device
28)American Standard Code for Information Interchange (ASCII, pronounced ask'
-ee ).
29) parity code An error detection code using one additional parity bit
30) Typical 8-bit microprocessors like the 6502 and the 8085 use software
multiplication and division
31) full-adder is A logic circuit with three inputs and two outputs. The circuit adds
3 bits at a time, giving a sum and a carry output
32) half-adder is A logic circuit with two inputs and two outputs. It adds 2 bits at
a time, producing a sum and a carry output.
33) Propagation delay is the time required for a signal to pass from the input of a
circuit to its output
34) it has only one stable state, the circuit is characterized by the term
monostable multivibrator, or simply monostable. a monostable switching circuit
(sometimes called a one-shot)
35) fall time is The time required for a signal to transition from 90 percent of its
maximum value down to 10 percent of its maximum.
36) rise time is The time required for a signal to transition from 10 percent of its
maximum value up to 90 percent of its maximum.
37) A flip-flop is one such circuit, and the characteristics of the most common
types of flip-flops used in digital systems are considered in this chapter. Flip-flops
are used in the construction of registers and counters, and in numerous other
applications. The elimination of switch contact bounce is a clever application
utilizing the unique operating characteristics of flip-flops. In a sequential logic
circuit flip-flops serve as key memory elements
38) A flip-fiop is a bistable electronic circuit that has two stable states-that is, its
output is either O or +5 V dc. Flip Flops are also know as latch.
39) asynchronous Independent of clocking. The output can change without
having to wait for a clock pulse.
40) latch Another term for an RS flip-flop.
41) synchronous When outputs change states in time with a clock. A clock signal
must be present in order for the outputs to change states
42) A register is simply a group of flip-flops that can be used to store a binary
number. "There must be one flipflop for each bit in the binary number
43) A mod-2 counter consists of a single flip-flop; a mod-4 counter requires two
flip-flops, and it counts through four discrete states. Three flip-flops form a mod-
8 counter, while four flip-flops form a mod-16 counter. Thus we can construct
counters that have a natural count of 2, 4, 8, 16, 32, and so on by using the
proper number of flip-flops.
44) a mod-7 counter requires three flip-flops, since 8 is the lowest natural count
greater than the desired modified count of 7.
45) natural count is The maximum number of states through which a counter can
progress. Given by 2n, where n is the number of flip-flops in the counter.
46) the Circuit settles at two different states generating two different set of
outputs. Such a situation is called critical race condition and is to be avoided in
asynchronous sequential circuit.
47) Two simple but important tests that can be performed to check the proper
operation of the DI A converter are the steady-state accuracy test and the
monotonicity test.
48) The simple fact that the ladder voltage has steps in it leads to the digital
error in the system. The smallest digital step, or quantum, is due to the LSB and
can be made smaller only by increasing the number of bits in the counter. This
inherent error is often called the quantization error and is commonly ± 1 bit.
49) quantization error is The error inherent in any digital system due to the size
of the LSB.
50) A dc power supply is required to energize any semiconductor memory chip.
Once de power is applied to a static RAM (SRAM), the SRAM retains stored
information indefinitely, without any further action. A dynamic RAM (DRAM), on
the other hand, does not retain stored data indefinitely; any stored data must be
stored again (refreshed) periodically. Both SRAMs and DRAMs are used to
construct the memory inside a microcomputer or minicomputer
51) The information (data) stored in a ROM is .fixed and will be retained
permanently even if de power is removed. Clearly, a ROM is ideal for storing
permanent instructions necessary for the startup and operation of a computer.
These instructions are retained, even when the computer is off, and become
immediately available each time the computer is turned on. Data stored in a
programmable ROM (PROM) is permanent-a PROM can be programmed only
once! However, the data stored in an erasable PROM (EPROM) can be "erased";
the
EPROM can then be used to store new data. PROMs can be either bipolar or MOS,
but all EPROMs are MOS.
52) A floppy disk is formed by the deposition of magnetic material on a semirigid
plastic disk housed in a protective cover.
53) Double-sided high-density 5.25-in disks have a capacity of 1.2 MB. Double-
sided high-density 3.5-in disks have a capacity of2.88 MB.
54) The memory capacity of a CD is in the range of 650-700 MB, i.e. nearly 500
times more than 1.44 MB magnetic floppy disk.
55) Its newer variety called Digital Versatile Disk (DVD) can store data from 4.7
GB to 17.1 GB depending on configuration and make.
56) Single sided, single layer has capacity of 4. 7 GB, single sided double layer
has 8.5 GB, double sided single layer has 9 .4 GB while double sided double layer
has 17 .1 · GB of storage space. The better quality of DVD output compared to
CD comes from better channel coding; error correction scheme and of course a
higher data transfer rate
57) address Selection of a cell in a memory array for a read or a write operation.
• cache Small, fast SRAM, a faster memory as an adjunct to slower main
memory.
CAM Content Addressable Memory.
58) flash memory A kind of nonvolatile memory which can be written and erased
electrically.
• Floppy disk A movable low capacity magnetic storage media.
59) The propagation delay time is the time it takes for the output of a gate to
change after the inputs have changed. The propagation delay time of a TTL gate
is approximately 10 nanoseconds (ns).
60) When you switch a transistor from on to off, you have to wait for the extra
carriers to flow out of the base. The delay is known
as saturation delay time. One way to reduce saturation delay time is with
Schottky TTL.
61) The maximum number of TTL loads that can be reliably driven under worst-
case conditions is called the fanout. With standard TTL, the fanout is 10 because
one TTL driver can drive IO TTL loads.
62) A floating CMOS input is poor in design because it produces large power
dissipation. 63) certain number of bits are allocated that defines the instruction
to be executed. This is called operation code or in short, opcode. The rest of the
bits can be used for referring the memory .location from which data is to be
brought or stored, if required by the instruction.
64) Memory Address Register (MAR) is a 5-bit register that stores the address of
the memory location referred in a particular instruction. The output of this is fed
to a 5-to-32 address decoder. Each output of the decoder points to a location in
the memory. All memory referenced instruction loads memory address in MAR.
Memory Data Register (MDR) is an 8-bit register that stores the memory output
when a memory read operation is performed. During memory write operation it
stores the value that gets written to the memory. Thus it can also be called a
memory buffer.
65) Program Counter (PC) is a 5-bit counter that stores the address of the
memory location from which next instruction is fetched
66) memory address register A register that contains address of memory
location for all memory referenced instructions.
• memory data register A register that acts as buffer between memory and rest
of the circuit, storing data that moves to and from memory
67) program Series of instructions that accomplishes a task in a computer.
" program counter A register that stores address of next instruction.
