Specifications

THEORY OF OPERATION

Since many host systems and applications have unique formats and protocol

requirements, the IS4920, just like all other Metrologic scanners, supports a wide

range of configurable features that may be selected by scanning a corresponding

scanner-programming barcode from MetroSelect Single Line Configuration Guide

and Area Imaging Barcode Supplemental Configuration Guide, both available for

download from the Metrologic web-site www.metrologic.com.

Usage of the Host Interface Signals

In the default “multi-try” trigger mode of operations, the scanning engine is

activated by the nTrig signal, which must be kept active (low) until the successful

scan is achieved, as indicated by the nGoodRead signal.

Upon a successful scan, the IS4920 asserts the nGoodRead signal and keeps it

asserted (low) for the duration of transmission of the decoded data to the host, or

for the minimum of 100 msec (configurable to 50 msec), which coincides with the

duration of the nBEEPER signal.

The nGoodRead and nBeeper signals are driven with LVC family open drain

outputs powered 3.3V typical and pulled up on the decode board with 100K

resistors. The default state of these pins is Hi-Z (pulled up via 100K) and these

signals are capable of sinking up to 24mA each when driven to the low state. For

beeper applications, care must be taken to ensure that inductive spikes do not

cause the voltage on the lines to exceed the maximum voltage of 5.5V.

At any given time, the IS4920 can be in one of the following power modes:

• Boot Mode

• Operating Mode

• Idle Mode

• Sleep Mode

• Presentation Wakeup Mode

• Power-down Mode (TTL Decode Only)

• Suspend Mode (USB Decode Only)

When the scanner is in the Sleep or Presentation Wakeup Mode, the nWake or

nTrig signals can be used to wake up the scanner.

The nWake signal wakes up the scanner and turns the scanner into the Idle

Mode, which in the IS4920-xx103 TTL RS232 version enables communication

with the host for a short period of time defined by the value of the sleep timeout,

which is set to 1 second by default. (Note that in the IS4920-xx38 USB version

configured for USB Serial Emulation Mode, communication with the host is

enabled even when the scanner is in the Sleep or Presentation Wakeup Mode.)