© 2000 Ubicom, Inc. All rights reserved. - 22 - www.ubicom.com AN16 SX IrDA Virtual Peripheral Implementation 4. 2 SX TO SX COMMUNICATION 4.2.1   SX to SX Application Description The ‘SX 2 SX’ sample application allows SX devices to
initiate XID discovery and send unreliable broadcast data
packets.  The  SX  is  controlled  by  commands  received
from the debug port as follows:
•    ‘d’ will start the discovery process
•    ‘c’ will broadcast the value of port c (raw byte).
•    ‘s’ will broadcast a hello string.
The  SX  will  respond  to  the  command  with  a  ‘^’  on  the
debug port if it has accepted the request or a’!’ if it has
refused the request. A request will be refused if IR com-
munication  has  been  detected  in  the  past  500  ms  (as
required by the IrDA IrLAP specification to prevent colli-
sions).
Note  that  this  connectionless  protocol  does  not  require
the LMP layer and could be implemented with much sim-
plified  LAP  and  payload  layers  freeing  up  over  half  the
code space. 4.2.2   Requirements •    Two SX boards (at least) each with a serial connection       to a PC through the debug ports.
Note:The serial cable should be a straight-through cable
with at least TX, RX, and GND connections. 4.2.3  Operation •    Open a terminal program on the appropriate physical       COM port at 115200,n,8,1, no handshaking on each of
      the computers.
•    Power up the SX boards. Power is indicated by the       ‘PWR’ LED.
•    Press ‘d’ on one computer to request that the discovery       process be initiated. The SX should respond with a ‘^’
      followed by the text names of all the IrDA devices in
      range. If a ‘!’ is returned then other IR communication
      has been detected so the request cannot be accepted.
•    Observe the LEDs during the discovery process. The       initiating SX’s TX indication LED should be flickering for
      about one second and any responses should be seen
      with the RX indication LED. The response will occur at
      different intervals through the transmission process
      each time as a different random reply slot will have
      been chosen by the responder.
•    Press ‘c’ on one computer to request that the contents of port c be broadcast. The SX should respond with a
‘^’ and all other SX devices in range should display the
received byte. If a ‘!’ is returned then other IR commu-
nication has been detected so the request cannot be
accepted.