SECTION 3
OPERATION
3.1 INTRODUCTION
This section explains operating information for the Interface. It describes its theory of operation, timing,
commands, operating modes, and responses.
3.2 THEORY OF OPERATION
The Interface has 3 main functions: 1) monitor the SIGNAL inputs from the Readers for the presence of
Electronic Tag data, 2) generate pulses on the ENABLE lines to control the Readers so that only one is
enabled at any time, and 3) communicate over the serial interface to meet the specific needs of the user.
The Interface controls Reader operations by issuing 3 different types of pulses on the ENABLE lines.
The pulses are differentiated by their duration and have the following effect:
Microseconds
PULSE Min Max DESCRIPTION
RESET 2.0 3.0 Disables all Readers.
READ 1.0 1.6 Indicates valid Tag Read.
INCREMENT 0.3 0.8 Sets and Increments Reader Addresses
The Interface normally provides +5V DC (nominal) at the ENABLE output and 0 to 0.5V DC at the
ENABLE RETURN outputs. Pulses are generated by momentarily raising the ENABLE RETURN
output to +5V DC. The Interface performs its multiplexing by first generating a RESET pulse. Upon
detection of the RESET pulse, all Readers disable themselves for the duration of the pulse. When the
pulse is terminated, Reader #0 is left enabled and the Interface checks its SIGNAL inputs for valid data.
If it detects signals at this point it knows that the Tag is at Reader #0. The Interface then generates an
INCREMENT pulse that disables Reader #0 and enables Reader #1. The Interface continues enabling
Readers and checking for data until all Readers have been checked then starts the loop again.
The Interface can be instructed, via the serial interface, to ignore certain Readers in which case it
generates two consecutive increment pulses at the appropriate Reader address, without checking the
SIGNAL inputs in between. Normally, the Interface looks at the SIGNAL inputs for a minimum of 14
milliseconds. If it sees a Tag during this time, it will extend the interval until the next INCREMENT
pulse, to finish reading the Tag.
If the Interface detects a Tag, it generates a READ pulse. The Readers generate a read indication upon
detection of this pulse and it also functions to increment the active Reader just like the INCREMENT
pulse.
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