74147 Encoder is a priority encoder IC. 74LS147 provides priority decoding of the inputs to ensure that only the highest order data line is encoded. Both devices have data inputs and outputs which are active at the low logic level.The LS147 encodes nine data lines to four-line (8-4-2-1) BCD. The implied decimal zero condition does not require an input condition because zero is encoded when all nine data lines are at a high logic level. A keypad provides an easy input device to a digital circuit. It consists of several switches, one under each key, which have one of their two poles in common. To use a key to send a HIGH (1) signal, one must connect the common pin to 5 volt supply and put a resistor to ground from each of the other pins, as with the DIP switch package. Using 16 individual resistors to do this it would be rather tedious, so we will once again use the resistor arrays. The particular resistor array which we will use has several resistors in it which all have one end in common.

However; in some cases, such as in this lab, you will be using the keypad for input to devices which use active low inputs. This means that you will want a key pressed to give a low output on the corresponding line. To do this, simply switch the common connections of the keypad and resistor array mentioned above. This means you will connect the common pin of the keypad to ground and the resistor array to Vcc (+5V).