Background

Palm Pilots and HP 82240 printers both have infrared ports. Like a TV remote control, they send signals through the air by flashing pulses of infrared light. But Palms use very short pulses and remote controls tend to send longer pulses. Also, the two devices group their pulses together in different ways.

The format that a remote control uses is similar to the format used by 82240 printers. They are known as Consumer Infrared (CIR). CIR uses a carrier signal. An example of a carrier signal is shown below…. (show a 1 bit)

For example, the 82240 sends a binary '1' bit by sending about 210 microseconds (uS) of carrier signal followed by 630uS of silence.

Palm Pilots don't use CIR. Most Palm hardware isn't designed to generate a carrier signal. The format Palms use to send data over infrared is called IrDA. IrDA is actually a multilayered protocol, with higher layers providing special features that make it easy to do things like exchange business cards in a universal format. We're interested in the lowest layer, the way individual bytes are sent. This layer of IrDA is called Serial IR (SIR).

Serial IR is almost what it sounds like. When transfering data over a cable connected to a serial port, the basic format used to send a byte looks like this:
(NRZ diagram)

There is the option to choose the number

(IrDA diagram)

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-Share Alike 2.5 License.