IBM 4400 manual Security Level

Chapter 7 Bar Codes

PDF 417

The PDF417 structure is shown in Figure 18 and described below.

SR, SC

POSITION UPPER GUARD BAND

QUIET START ZONE CODE

DATA FIELD

STOP	QUIET
CODE	ZONE

LOWER GUARD BAND

Figure 18. PDF417 Structure

Quiet Zone

Both ends of the bar code structure require blank quiet zones. The quiet zones must be at least 0.25 inches wide and completely blank to ensure accurate reading of the start/stop codes and to prevent adjacent bar codes from overlapping. Be sure to provide sufficient space on the form for the quiet zones.

Start/Stop Codes

The start/stop codes identify the leading and trailing end of the bar code.

Data Field

PDF417 provides twelve modes to encode data. The first three are pre- established (the remaining nine are user modes, which can be defined by users or industry associations according to specific applications):

1.Extended Alphanumeric Compaction mode (EXC). Comprised of four sub-modes, this mode offers encodation of all printable ASCII characters. This is the default mode; ASCII Emulation uses shift or latch characters to enable other modes.

2.Binary/ASCII Plus mode. This offers encodation for all ASCII characters, printable or not, and binary values.

3.Numeric Compaction mode. This offers encodation for numeric values to a density of almost 3 digits per code word.

ASCII Emulation will automatically switch between modes to provide the smallest encodation for the data.

Security Level

PDF417 can detect and correct errors. Each label has 2 code words of error detection. You can select the error correction capacity based on application needs. Specify a security level in the range of 0 - 8, at the time of printing.

PDF417 can also recover from omissions and misdecodes of code words. Since it requires two code words to recover from a misdecode, one to detect

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