Issue
139 February 2002
What
Good is IrD, Eh?
Part
2: Wireless Communication
byJeff
Bachiochi
IrLAP/IrPHY
Frames
Each phase of
an IrLAP/IrLMP service procedure requires one or more
IrLAP/IrPHY frames. A frame is a formatted data or control
transmission between IrDA devices. The IrLAP assembles/disassembles
the frame and the IRPHY sends and receives it via IR.
The frame consists of a beginning-of-frame character (BOF),
the payload, a frame check sequence (FCS), and a finish-of-frame
character (FOF). The payload consists of the address,
control, and optional information fields.
The address
is a 7-bit (left-justified) address identifying a particular
link between two devices. The least significant bit is
a command/response bit and is set during a primary (initiator)
transmission and clear during a secondary (responder)
transmission. (So, odd addresses are from the primary
device and even addresses are from the secondary.) The
Control field defines the function of the frame. The information
field’s existence is dependent on the Control field.
