User's Manual

708UM0210-01 October 1999 Autotag-P User Manual Page: 14 of 33
Summary of important points about RF:
• RF is unable to penetrate most metals. (For example, talking to someone in a room with metal walls over a
hand held radio is impossible. RF can however go around the walls.)
• RF may be reflected by walls and other structures, especially those with metal reinforcing.
• RF becomes weaker with distance.
4.2. Autotag-P Communications Architecture
Communication between the Tag and Base Station takes place as follows:
As stated in the Introduction (Section 1.) there are two ways of configuration. These depend on site conditions
and requirements in terms of functionality.
1. An arming input is provided. This is a relay input and the triggering device could be a loop detector,
mass detector or some similar device. This allows for triggering of the Base Station only when a vehicle
is present. The Base Station is then only transmitting at such times. The advantages of using this are:
- It reduces the chance of false triggering (eg. by a pedestrian walking past with a Tag).
- The intermittent transmission reduces possible interference with other devices that may be
operating at the same frequency in the vicinity.
- The time-averaged radiation from the device is greatly reduced. This may in some cases be
important for compliance with local EMC regulations.
2. Should the arming input not be used, the Base Station will continually transmit a signal. The advantages
of this are:
- The Tag is triggered as soon as it comes within range, and sensitivity to nulls is reduced.
- The loop or other triggering device is made redundant, reducing the system and installation
costs.
The following applies to both configurations:
The Base Station transmits a signal to any Tags within range. The Tag is activated by this signal. It then checks
to see that it is actually a Base Station that has woken it up. It does this by decoding the code that was
transmitted. Once satisfied, it then transmits its own 32 bit code. The code is received and checked for integrity
by the Base Station and then passed on to the control system via the communications connector.
4.3. Coding
The coding in the Autotag-P system is split into the following sections:
32 bit User Data (Tag only)
16 bit Installer code
8 bit Distributor / OEM code
32 bit mask (Base Station only)
4.3.1 32 Bit User Data (Tag only)
The 32 bit User Data can be programmed into the Base Station and Tag using the Autotag-P
Programming Station. The 32 bits of User Data can be programmed in any combination of site code
bits and card number bits to match the access controller’s requirements.
This feature makes the Autotag-P system very flexible, enabling configuration to most access
controllers.
For more information on Programming the 32 bit user data, refer to the Autotag-P Programming Station
User Manual Document Number 708UM0201.
The Autotag-P Tags are shipped from the factory with the 32 bit User Data set to the Tag’s serial
number.