Specifications

OPERATIONAL TIMING

The TTL version of the IS4920 does not have an on board microcontroller to

control the power to the decode platform. As such, the power can only be

supplied to the decoding platform in response to a signals applied by the host

(Trigger or Wake). On power up, if both of these signals are high the power will

not be applied to the decoding platform and the board will be in the Power Down

mode. The Power Down signal will be high and all other host I/O will be in the

idle state. In order to apply power to the decode either the Trigger or Wake signal

need to be held low until the Decode processor can take over control of the

power switch. Once the decoding processor takes control of the switch, the

Power Down signal will be brought low and the Trigger and Wake signals can be

used with out interrupting the power.

Power Down / Suspend / Power Removed

At any time VIN can be completely removed from the IS4920 however, care must

be taken to avoid removing power during Boot up, Flash upgrade, or

Configuration change as this could cause corruption to the Flash memory and

result in Program and or Configuration corruption. Figure 15 shows several host

signals during a power remove condition for the USB.

The IS4920-TTL enters into the power down state in which power to the decode

platform and imaging engine is removed. The decoding processor can initiate a

power down sequence one the software configurable power down time has

elapsed. Note, the device will only enter power down if the Trigger and wake

signals are high.