User's Manual

Optimizing MPI 6000 Reader System Performance
5-9
Note: The TDM synchronization period is set in 1.0-millisecond increments, and the
TDM delay and TDM duration are set in 0.5-millisecond i
ncrements.
The TDM example shown in Figure 5-4 and Table 5-3 was designed with three time
slots; however, two time slots can be used instead depending on the number of
frequen
cy channels and the timing. Implementing TDM with three time slots reduces
the time avaliable for a transaction in a given lane by a factor of three. Similarly,
implementing TDM with two time slots reduces the time avaliable for a transaction in
a given lane by a factor of two. Although it is possible to implement four or more time
slots, it is unlikely that more than three time slots are necessary or beneficial.
TransCore recommends that a guard-band of 1
millisecond be used between each of
the time slots to ensure that the re
aders in the previous time slot have sufficient time to
settle before the readers in the next time slot become active. This procedure can be
done by setting the TDM delay on each reader to account for a duration that is 1 milli-
second longer than the actual duration and setting the TDM synchronization period to
a value that accounts for
a duration 1 millisecond longer than the actual duration.
All the readers designated as slave readers in the plaza on the same TDM bus are
depe
ndent on the synchronization signal from the master reader. In the event that the
synchronization pulse from the master reader stops functioning, or the TDM signal
from the master reader becomes disconnected from the rest of the readers in the plaza,
a provision in the readers allows a slave reader to serve as a backup master reader and
supply the synchronization pulse. Although this situation will cause the slave reader to
send an error message to the lane controller, the slave reader will continue to function
and provide the TDM synchronization pulse for the other operational readers on the
remaining TDM bus.
Because the location in the plaza where the sig
nal break may occur is u
nknown,
TransCore recommends that provisions for a break anywhere in the line be consid-
ered. Although the TDM synchronization period settings for the slave readers could
all be set at the same single value of 1 millisecond longer than the value
used for the
TDM synchronization period on the master reader, they should be set at unique values
increasing at 1 millisecond for each reader, starting at a value 1 millisecond higher
than that of the master reader. This setting ensures that only one reader will provide
the synchronization pulse to a given group of readers in the plaza remaining on the
Table 5-3 TDM Timing Settings
Time Slot TDM Delay TDM Duration
TDM Synchronization
Period
a
T1 0 ms (setting = 0) 9 ms (setting = 18) 31 ms (setting = 31)
T2 10 ms (setting = 20) 9 ms (setting = 18) 32 ms (setting = 32)
T3 20 ms (setting = 40) 9 ms (setting = 18) 33 ms (setting = 33)
a. Master reader TDM synchronization period equals 30 milliseconds.
PRELIMINARY