The task was to implement a circuit in logisim that controls an entry gate. The gate has 3 possible inputs; a £1 coin paid in, a £2 coin paid in or the cancel button pressed. The gate must store the amount of money paid in and has four possible behaviours for outputs. Once the gate has received £4 it must open, in terms of implementation a LED must light up and stay lit until another input is received, any extra money in the machine must count towards the next entry fee. The other behaviours are based off when the cancel button is pressed, a LED relating to the amount of money paid into the machine towards an entry fee e.g. a £1 LED if £1 is in memory etc. up to the maximum of £3, In the circuit these LED 's must stay on until the next input.
The general structure of my implementation can be split up into three segments; Input, storage, and output. In the input section there are 2 bits of memory to temporarily store the 3 different inputs, 01 representing £1, 10 representing £2 and 11 representing cancel pressed. This memory is cleared once it has been clocked into the main storage of the system. The storage is implemented with 3 bits of memory as there are 6 possible states for the memory, £0 to £5, the 1 and 2 bit are only affected once an input has been clocked in however the 4 bit is only affected by the carry bit of the 2 bit memory and is cleared as soon as an input button has been pressed as this was part of the assignment specification.