EE1A Part A Revision Notes

1
EE1A Part A Revision Notes

• What should you be expected to do in a typical
  exam question ?
• Understanding of basic principles.
• Ability to perform simple circuit analysis and/or
  design.
• Applying skills to unfamiliar problems.

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EE1A Part A Covered ...

• Number Systems
• Decimal, Binary, Hex.
• Binary Arithmetic
• Arithmetic Logic Units
• Addition circuits
• Subtraction circuits
• Flags
• ALUs

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EE1A Part A Covered ...

• Registers
• Using a Working Register with an ALU
• Tri-state ports Busses
• Microcontrollers
• Basic building blocks
• Special purpose registers
• Programs

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Revision Examples

• Convert the decimal numbers 53 and 21 into binary
  (base-2) form using eight digits.
• Calculate the twos complement representation of
  the decimal number 21.

5
Revision Examples

• Using the circuit shown below, what is the
  relationship between the three bit output number,
  Q0-2, and the pair of inputs A0-2 and B0-2 when
• The control input is low.
• The control input is high.

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Revision Examples

• The figure below shows a positive edge triggered
  D-type flip-flop acting as a simple one bit
  information store. Copy the D, CLK signals and
  draw the missing Q signal.

CLK
Q
D
Q
Answer At first rising edge of CLK we know that
Q must be low (because D is low here) at 2nd
rising edge D is high so Q must now go high. At
last rising CLK edge D is still high so Q must
stay high I(and remain high while D goes low
because there has not been a new rising edge of
CLK.
D
CLK
Q
7
Revision Examples
Briefly describe the three possible states of a
tri-state port and their use in connecting
devices to a common bi-directional bus.
Answer Low impedance, high (equivalent to a
ve d.c. voltage source.) Low impedance, low
(equivalent to a short circuit to ground.) High
impedance (equivalent to a large resistor
connected to ground.) In the two low impedance
states, the port can write to a common bus as
long as all other ports sharing the bus are in
the high impedance state. In the high impedance
state, a port can read from the bus or simply
ignore all bus activity.
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Revision Examples
In the context of a micro-controller, briefly
describe the functions of i. The Status
Register. ii. The Program Counter. iii. The
Working Register.

• Answer
• The status register is used to store the states
  of several flags (e.g. carry flag, zero flag)
  generated as a result of an arithmetic or logical
  operation.
• ii. The program counter holds the address, in
  program memory, of the next instruction to be
  executed.
• iii. The working register is used to store one of
  the operands to be inputted into the ALU and also
  stores the result of an arithmetic or logical
  operation.

9
Revision Examples
Outline the differences and the relationships
between assembly language and machine code.
Answer A program written in assembly language is
a list of human readable code. A machine code
program, on the other hand, is a list of numbers
understood by the control unit of a
microcontroller. All assembly language
instructions map onto a unique machine code
equivalent. To convert from assembly language to
machine code, an assembler is used.
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Revision Examples
The figure above shows an ALU, working register
and two general-purpose registers R0 and R1, all
connected to a common system bus. List the data
transfers required to add together the contents
of R0 to itself and store the answer in register
R1.

• Answer
• R0 outputs to the bus, W inputs and stores.
• R0 outputs to the bus (again), the ALU adds
  (storing the result in W)
• W outputs to the bus, R1 inputs and stores.

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Revision Examples
ii. List the data transfers required to compare
for equality the contents of registers R0 and R1,
the result appearing in the zero flag.

• Answer
• R0 outputs to the bus, W inputs and stores.
• R1 outputs to the bus, the ALU subtracts (storing
  the difference in W)
• The zero flag will now be high only if R0 R1