Specifications

OPERATIONAL TIMING

The following section describes the timing associated with the various operating

modes of the IS4920 including Power up, Power down, and Decoding (from idle

or Sleep). The waveforms shown in this section assume VIN = 3.3V, Good Read

pulled up with 10K resistor to VIN, and Beeper pulled up with 10K resistor to VIN.

Power Up / Boot Up

The power up sequence of the IS4920 depends on the interface type. For the

IS4920-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 scanner is

completely controlled by the on board USB controller per the USB spec. In this

version, only idle and sleep modes are supported. For additional power savings,

the unit must be placed in Suspend per the USB specification. The following

waveform shows the power up sequence of the USB version of the IS4920.

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 this waveform, it can be seen that the entire boot up

sequence takes approximately 9 seconds.

Figure 16. Power Up Sequence of USB Version