Metrologic Instruments IS4921 - Manual (Page 25)

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The nTrig signal not only wakes the engine up, but also immediately activates and turns the engine into the
Operating Mode.
Either nWake or nTrig signals can be used to restart the TTL RS232 scanning engine when the engine is in
Power-down Mode, which is indicated by the asserted (high) PWRDWN signal.
The PWDWN pin is used to indicate when the decode engine is in various operating modes such as Power
Down, Suspend, and Boot.
Note: The output signals from the decode engine can experience analog behavior when VIN is initially applied
or removed due to the supply voltage ramping up or down. Care must be taken to ensure that this
behavior does not adversely affect the host System. Special attention must be given to the PWRDWN
Pin. When power is initially applied, the output state of this line will be indeterminate for about 10mS
until the USB controller exits reset. The state of this pin should be disregarded during this time. The
following waveforms show several signals when VIN is first applied (Figure 17) and when VIN is
removed (Figure 18).
Figure 17. VIN First Applied (USB)
Figure 18. VIN Removed (USB)