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Application Note 16
SX IrDA Virtual Peripheral
The IrDA (Infra-Red Data Association) standard is wire-
less replacement for traditional wired connections
between computing devices and peripherals. It uses an
infra-red LED and photo-diode to transmit information at
up to 4Mbps over one metre.
This application note describes the implementation of the
lower levels of the IrDA protocol stack and the high level
IrComm protocol for a secondary device on the SX com-
munications controller. The implementation of this reli-
able protocol on a small communications controller is
achieved by relying on the applications ability to re-send
data upon request rather than the traditional use of large
The implementation communicates at up to 115.2kbps
and makes use of the SXs high clock speed to shape the
IrDA pulses without external hardware. It uses two virtual
peripheral UARTs: one for the IrDA port and one for a
debugging serial port.
The next section gives an overview of the IrDA stack and
describes the features of the SX implementation. Each
layer of the stack is then explained in detail. Finally,
descriptions of the demonstration applications and hard-
ware are given.
This documentation should be read in conjunction with
the IrDA Specification, IrDA Lite Specification and
IrComm available from www.irda.org.
THE IrDA STACK
Figure 1-1 shows the IrDA protocol stack. The boxes in
white are included in the SX implementation and are
described in this document
The physical layer converts octets of data to bit streams
and transmits them in the form of bursts of IR light (and
vice-versa). The rated operating range for IrDA is one
metre for all speeds, however under typical conditions
this range is usually higher.
The framing layer encapsulates the payload data within a
frame so that it can be transmitted and identified as a
frame of data when it is received by another station. The
frame data is protected by a CRC to confirm the validity
of the data.
1-1. IrDA Protocol Stack