Decode Timing

Engine image acquisition or decoding can occur from either the Idle Mode or the Sleep Mode. The process is initiated by asserting the nTrig signal (or serial command when in the Idle Mode). Once the trigger signal is received, the image sensor is reset and image acquisition begins. During image acquisition, the illumination LEDs are enabled for a time determined by the FirstFlash circuitry on the non-decode 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 decode engine receives a trigger signal while in the Sleep Mode, an additional delay is needed for the processor exit Sleep Mode and reconfigures the sensor.

Figure 25 and Figure 26 show the amount of time required for decoding when a nTrig signal is asserted in both the Idle Mode and Sleep Mode.

Notes: 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.

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

Figure 25. Decode time after receiving nTrig signal in Idle Mode.

Figure 26. Decode time after receiving nTrig signal in Sleep Mode.

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