__Digital logic__

NISECSpecimenPaperlNo8a

A drinks machine measures the size and the weight of each coin as it is entered. It only accepts any coin which has the correct size and the correct weight. Complete the table below using 1 for accept or 0 for reject.

Size not correct | Size correct | |

Weight not correct | ||

Weight correct |

Complete the truth table using the logic network given below.

A | B | C | D | E | F | G | output |

0 | 0 | 0 | 0 | ||||

0 | 1 | 0 | 1 | ||||

1 | 0 | 0 | 0 | ||||

1 | 1 | 1 | 0 |

A room has two doors and two windows. There is a burglar alarm system wired up using the following logic diagram.

(a) Explain the purpose of the logic in the diagram. (Assume that doors or windows being open and the alarm sounding are represented by a logical 1.)

(b) The logic gate labelled X is changed to an AND gate. Write down what bad effect this has.