User's Manual

April ’00 Chapter 3. Synchronization

3.2.5.3 Triggered Synchronization

Triggered Synchronization is a Master/Slave Synchronization Bus where there is just

a pulse signal. All readers are configured as masters, but it is only one unit or a trig-

ger pulse source that issues the synchronization pulse at suitable intervals for the re-

quired operations on the transponder.

The more complex version of this is known as a Timing Bus, when different time win-

dows are defined for different operations to be carried out, for example: If multiple

readers are required to read addressed pages of Multipage transponders, then to

write data back to the transponders, the timing bus would start a read window lasting

90 ms then initiate a time window of 320 ms for a write operation. In this way the dif-

fering times required for the two operations can be accommodated. At the same time

the readers would be instructed thru the communication interface, about which com-

mand to execute during each window. Therefore the slaves have to receive their

command before the master.

Advantages:

1. The master unit has total control over the coordination of the connected de-

vices and can allow ‘windows’ for particular operations.

2. Reading and Writing can be accommodated, if there is sufficient separation

to prevent data corruption during the Write process.

Disadvantages:

1. Cannot be used for addressing MP transponders if readers are close to-

gether as addressing conflicts can arise.

2. Carrier Phase synchronization cannot be used.

3.2.6 Carrier Phase Synchronization

In some applications it is necessary to use several charge-up antennas close to each

other. In these circumstance, the magnetic charge-up fields generated by different

antennas superimpose on each other and may cause a beat effect on the magnetic

charge-up field, due to the slightly different transmission phases of different Power

readers. This effect will not occur when the transmitters of different readers are op-

erated from the same oscillator signal.

This is Carrier Phase Synchronization where all of the readers in a system use the

same oscillator. Carrier Phase synchronization must be used whenever Gate or Stick

antennas are facing each other and if they are inside the distances D1 or D2 as given

in Table 27 (Figure 7 shows the places to measure D1 and D2). This ensures that

there will not be any “beat effect” between the antennas.

Note:

Remember that putting two antennas close together also changes

antenna inductance, so that the antennas may no longer be tuneable

to resonance.