Metrologic Instruments IS4921 - Manual (Page 32)

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Notes: In Figure 21 , the nGoodRead, nBeeper, and PWRDWN signals are high while in the Power Down
Mode.
The RTS Signal will be high in Power Down Mode regardless of the RTS polarity software
configuration. Also, the RTS signal may have the incorrect polarity when the device first enters Boot
Mode (Figure 23) or right before the unit enters Power Down Mode (Figure 24).
The USB version can be placed into Suspend Mode via the USB suspend signal for low current consumption.
When this occurs, power to the decoding platform and imaging engine is removed. While in this state,
nBeeper and nGoodRead will be in their default state (Hi-z with weak pull up). PWRDWN will be high and the
USB data lines will be in the Suspend Mode.
Power Down / Suspend / Power Removed
At any time VIN can be completely removed from the decode engine however, care must be taken to avoid
removing power during the boot up, flash upgrades, or configuration updates. Removing power during these
times can result in the corruption of the flash memory. Figure 18 shows several host signals during a power
removed condition for the USB version.
The TTL version enters into the Power Down Mode in which power to the decoding platform and imaging
engine is removed. The decoding processor can initiate a Power Down sequence after a programmable time
period has elapsed without any activity. Figure 24 shows the TxD, RTS, VIN, and PWRDWN signals when the
TTL enters into Power Down Mode.
Figure 24. Power Down for TTL