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Encompass 4 Reader System Guide
TransCore Proprietary.
7–124
649NN Set Synchronization Hold-Off Time
Command
#649NN
sets the time in milliseconds that the reader will hold off after getting (or sending if
it is the master on the bus) the synchronization pulse before it starts to run its IAG tag sequence. This
command is used in close combination with command
#648NN.
Command
#649NN
is applicable only if a
value other than
#64800
is entered for
#648NN
and is used only when the IAG tag protocol is enabled.
Entering a value of
#64900
(factory default)
disables this feature. Entering a value between
#64901
and
#6490A
(hex value of 10 decimal) causes the reader to hold off starting its tag protocol transaction for
the time set between 1 and 10 milliseconds. This feature is used to lessen the possibility of a reader reading
an IAG tag that is activated by another reader in the site. Because IAG tags are battery powered active
transmitters, their read zones can be much harder to control than for beam-powered passive tags. The
pattern also will vary greatly among tags depending on the condition of the individual tag battery. If this
feature is used, each reader on the bus needs a value of between
#64901
and
#6490A
entered for the
feature to work. As with the
#648NN
command, the reader’s physical location on the bus is not critical,
but TransCore recommends that the reader numbering follow a logical sequence. Using this command,
more than 1 reader on the bus can have the same value, but TransCore recommends using all 10 slots
before reusing them. Command
#582
displays the Synchronization Hold Off Time.
Table 35 l
ists an example of a plaza having five Encompass 4 Readers in lanes where multiple readers
identifying the same tag would present a system problem. All of the readers are cabled together on a
synchronization bus (
). The example timing for
#648NN
is appropriate assuming IAG is the only
protocol enabled in all readers. The RF for all readers is set to 915.75 (
#6470DF
) and in this example it is
determined that an IAG attenuation setting of 9 dB (
#64609
) prevents a reader from activating a tag in an
adjacent lane.
Figure 50 Synchronization Bus Wiring
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