There are four inputs to the card reader: inputs X,Y, and Z are used to validate the correct door code, and input V is used to check if the card reader is still valid. After the card reader is being read by the system,there are three outputs to this system: alarm (A), door open (D), and Error (E). The circuit has the following functions:
The alarm (A) will trigger when the door code is incorrect.
Door (D) will only open when the decimal value of the binary inputs (x, y) is odd AND the card reader is valid.
The Error (E) signal goes on when the door code is correct (i.e. decimal value equal to odd) but the card is no longer valid (invalid card).