https://techdocs.altium.com/display/FPGA/NEC+Infrared+Transmission+Protocol

he NEC IR transmission protocol uses pulse distance encoding of the message bits. Each pulse burst (mark – RC transmitter ON) is 562.5µs in length, at a carrier frequency of 38kHz (26.3µs). Logical bits are transmitted as follows:

• Logical '0' – a 562.5µs pulse burst followed by a 562.5µs space, with a total transmit time of 1.125ms

• Logical '1' – a 562.5µs pulse burst followed by a 1.6875ms space, with a total transmit time of 2.25ms

When transmitting or receiving remote control codes using the NEC IR transmission protocol, the WB_IRRC performs optimally when the carrier frequency (used for modulation/demodulation) is set to 38.222kHz.

  When a key is pressed on the remote controller, the message transmitted consists of the following, in order:

• a 9ms leading pulse burst (16 times the pulse burst length used for a logical data bit)

• a 4.5ms space

• the 8-bit address for the receiving device

• the 8-bit logical inverse of the address

• the 8-bit command