Specifications

OPERATIONAL TIMING

The IS4920-USB can be placed into suspend mode via the USB suspend signal

in order to achieve low current consumption. When this occurs, power is

removed to the decoding platform and imaging engine.

Decode Timing

In the IS4920 image acquisition / decoding can occur from either the idle state or

the sleep state. This process is initiated by asserting the nTrig signal (or serial

command when in the idle state). Once the trigger signal is received, the image

sensor is reset and image integration begins. During image integration, the

illumination LEDs are enabled for a time determined by the First Flash circuitry

on the IS4910 engine. The image is then transferred to the processor and

decoded. Upon decoding the image, the processor asserts the nGoodRead

signal (low) and beings transmitting the decoded data. When the IS4920 receives

a trigger signal while in the sleep state, an additional delay is needed for the

decoding to processor exit sleep mode and reconfigures the sensor. The

following waveforms show the amount of time required for decoding when a nTrig

signal is asserted in both the idle state (Figure 17) and Sleep State (Figure 18).

Note: the total image acquisition / decode time can be approximated by

measuring the time from the nTrig signal going low to the nGoodRead signal

going low. This time will vary slightly based on several factors including code

quality, code type, and distance from the engine. The following waveforms show

a typical condition.

nTrig signal must be kept low for at least 20msec.