App note from Holtek on their dedicated IR remote IC. Link here (PDF)

The HT62104 is a high performance infrared remote encoder capable of encoding a signal with a 3-bit start code, 2-bit custom code and 7-bit data code. The HT62104 device has 8 key inputs. When one of the keys is triggered, the programmed code is generated and transmitted via an IR (38kHz carrier) transmission medium.