User Manual

Chapter 8 System Parameters and Comm ands
- 132 - Hi-G-Tek Ltd. Micro electro nic s & A sset Tra cking Techno logy
8
System Parameters and Commands
This chapter describes the details of the communications with the DataSeal
and the DataReader. Even though Hi-G-Tek publishes the RS-232/485
protocol of the DataReader, and part of the RF protocol, this manual does
not cover these details. Instead, it describes the commands and the
parameters in a more conceptual way, with syntax and examples in Visual
Basic as they can be used through the DataSealLib COM library. Note
there's also an online help that is supplied with the library. T his online help
is more technical than the explanations in this chapter: while this chapter
explains the concepts, the online help describes the COM interface in more
details.
8.1 The High Frequency RF Protocol
8.1.1 The Basics
In order to conserve power, the DataSeal is "asleep" most of the time. It
only opens its High-Frequency receiver for a short time every
predetermined period – usually 3 seconds. This fact has some implications
on the RF protocol as explained below.
The interval in which the DataSeal opens its receiver is determined by a
configurable parameter called Tw (which its default value corresponds to
about 3 seconds). Because the DataSeal listens to the RF only in this
intervals, if a DataReader wants to communicate with that DataSeal, it must
transmit a special signal called Reader Interrogation Header, that is at least
in the duration of Tw , in order for the DataSeal to receive it. When the
DataSeal receives this signal (in the short period that its receiver is open), it
knows that a command should follow, and it waits for that command. After