Metrologic Instruments IS4921 - Manual (Page 30)

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Operational Timing
The following section describes the timing associated with the various operating modes of the decode engine
assembly including Power Up, Power Down, and Operating (from Idle or Sleep). The waveforms shown in this
section assume VIN = 3.3V, nGoodRead pulled up with 10K resistor to VIN, and nBeeper pulled up with 10K
resistor to VIN, unless otherwise noted.
Power Up / Boot Up
The power up sequence of the decode engine depends on the interface type. For the USB version, a USB
Microcontroller controls the power to the decoding platform and imaging engine via a power switch. When
power is initially applied, only the USB controller is active and begins the process of enumeration. Once
enumeration is complete, the USB controller turns power on to the imaging engine and decoding platform. As a
result, powering up the engine is completely controlled by the on board USB controller per the USB
specifications. In this version, only Idle and Sleep Modes are supported. For additional power savings, the unit
must be placed in Suspend Mode per the USB specification. Figure 20 shows the power up sequence of the
USB version of the decode engine.
Note: The PWNDWN signal remains high until the Decode platform transitions to Idle Mode and is ready to
accept commands. In the USB version, the PWNDWN Pin will only be high during this boot up condition
or when the Decode enters, Suspend Mode. From Figure 20 , it can be seen that the entire boot up
sequence takes approximately nine seconds.
Figure 20. Power Up / Boot Up Sequence of USB Version