Symbol LS 1220 Product Reference Manual page 20

Introduction
Decoder
The Decoder contains a micro-controller that provides the capability for bar code decoding,
host I/O interface protocol, and other decoder functions.
The micro-controller contains a watchdog timer. The enabling/disabling and maintenance
of this watchdog are totally internal to the decoder; the host can not configure the watchdog.
The Decoder's reset circuitry holds the micro-controller in reset after power up to allow
sufficient time for hardware initialization. This reset period is 70 msec. nominal at 5 V dc. A
reset can occur upon power up, or power supply voltage falling below 2.8 V nominal. A reset
time is generated in the CPU from an external resistor, capacitor, voltage detector, and
internal pull-up resistor.
The non-volatile memory stores the Decoder capability parameters. After every reset, the
decoder checks for faults in the memory; if no faults are found, its contents are copied into
its internal RAM. If a fault is found, the decoder copies factory default values into RAM and
the memory. The Decoder does not correct the fault unless requested by the host.
Visible Laser Diode
The VLD (Visible Laser Diode) is a semiconductor device that emits laser light. The laser
output is different from conventional light sources in that it is coherent, both spatially and
temporally. The VLD output can be focused to allow barcode scanning over long distances.
Laser Driver
The Laser Driver is an electronic feedback circuit that controls the laser diode operation.
The circuit monitors and controls the VLD, providing a regulated optical output power level.
Mylar Motor
The Mylar Motor and Mirror Assembly is an electromechanical resonant scan element. The
oscillating motor/mirror assembly deflects the laser beam across the barcode to be
scanned. The resonant design minimizes power consumption, which is especially
important in battery operated applications. The scan element has been designed to be
highly rugged and reliable.
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