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Application Note 16 November 2000 SX IrDA Virtual Peripheral Implementation 1.0 Introduction 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 application’s ability to re-send
data upon request rather than the traditional use of large
data buffers.
The  implementation  communicates  at  up  to  115.2kbps
and makes use of the SX’s 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.
1. 1 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.
Figure 1-1. IrDA Protocol Stack IAS Tiny TP OBEX IrLAN IrCOMM IrLMP IrLAP Frame/Driver Physical Layer