EE1A Revision 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.

EE1A Revision Number Systems Decimal, Binary, Hex. Binary Arithmetic Arithmetic Logic Units Addition circuits Subtraction circuits Flags ALUs

EE1A Revision Registers Using a Working Register with an ALU Tri-state ports & Busses Microcontrollers Basic building blocks Special purpose registers Programs

EE1A Specimen Paper 5(c) Showing all your working, (i)Convert the decimal numbers 53 and 21 into binary (base-2) form using eight digits. (ii)Calculate the two’s complement representation of the decimal number –21. (iii)Using your answers from (i) and (ii), calculate using binary long addition, the result of subtracting 21 from 53. Show all working again.

EE1A Specimen Paper 5(d) Using the circuit shown in figure 6, what is the relationship between the three bit output number, Q 0-2, and the pair of inputs A 0-2 and B 0-2 when: (i)The control input is low. (ii)The control input is high. Figure 6

4 (a) Briefly describe the three possible states of a tri-state port and their use in connecting devices to a common bi-directional bus. EE1A Specimen Paper 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.

4 (b) In the context of a micro-controller, briefly describe the functions of: i.The Status Register. ii.The Program Counter. iii.The Working Register. EE1A Specimen Paper i.The status register, SR, 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, PC, holds the address, in program memory, of the next instruction to be executed. iii.The working register, W, 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.

4 (c) Outline the differences and the relationships between assembly language and machine code. EE1A Specimen Paper 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.

4 (d) Figure 4 shows an ALU, working register and two general-purpose registers R 0 and R 1, all connected to a common system bus. i.List the data transfers required to add together the contents of R 0 to itself and store the answer in register R 1. EE1A Specimen Paper 1.R 0 writes to the bus, W reads and stores. 2.R 0 writes to the bus (again), the ALU adds (storing the result in W) 3.W writes to the bus, R 1 reads and stores.

ii. List the data transfers required to compare for equality the contents of registers R 0 and R 1, the result appearing in the zero flag. EE1A Specimen Paper 1.R 0 writes to the bus, W reads and stores. 2.R 1 writes to the bus, the ALU subtracts (storing the difference in W) The zero flag will now be high only if R 0 = R 1