Product manual

Protocol Level
67
CAD Command with Retry
When CAD sends a packet which does not change the state of the Model 6 or any of its
units, such as a request for the status of a certain station transponder, the following
sequence takes place. If the Model 26 does not respond immediately with an LLACK, the
CAD will re-transmit the request. If the Model 26 responds with an LLACK and the
wrong LLSEQ#, the CAD will re-transmit the request. We recommend that the CAD
periodically conducts an audit or update regarding the status of all stations and units
when available to prevent a lost message from faulty information in the CAD related to
the availability of a unit or the status of a station.
tm Transmitted from CAD to M26 Response from M26 to CAD
t0 Stn Full Status Req.02 HL23,LL 00>
t1 Nothing for 2 seconds
t2 Stn Full Status Req.02 HL23,LL 00>
t3 <LLACK FF
t4 Stn Full Status Req.02 HL23,LL 00>
t5 <LLACK 00
tN A significant time may elapse here A significant time may elapse here
tN+1 <Station Full Status HL 23,LL FF
tN+2 Nothing for 2 seconds
tN+3 <Station Full Status HL 23,LLFF
tN+4 LLACK FF>
tN+5 <High Level ACK HL 23,LL 00
tN+6 LLACK 00>
CAD Command Unit State Control
When the CAD sends a unit state control command which causes a change in the state of
the Model 6 transponder, the interchange is as shown below. The status returned will be
status 3 format 1 for unit/station status. The status is returned before the HLACK is sent.
tm Transmitted from CAD to M26 Response from M26 to CAD
t0 Unit State Control 00, HL34,LL FF>
t1 <LLACK FF
tN A significant time may elapse here A significant time may elapse here
tN+1 <Stn Status 03-1,HL 34,LL FF
tN+2 LLACK FF>
tN+3 <High Level ACK HL 34,LL 00
tN+4 LLACK 00>