IBM 4400 manual Code 128A Data Field

Code 128

Code 128

The Code 128 structure is shown in Figure 10 and described below.

			OPTIONAL
			CHECK DIGIT
SR, SC
POSITION
		UPPER GUARD BAND
QUIET	START	DATA FIELD	STOP	QUIET
ZONE	CODE		CODE	ZONE

HEIGHT

LOWER GUARD BAND

OPTIONAL READABLE DATA FIELD

Figure 10. Code 128 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. Each of the Code 128 subsets uses a unique start code and a common stop code, both automatically provided by the ASCII Emulation.

Code 128A Data Field

Subset A operates in the manual mode only. Subset A data characters include mostly normal printable ASCII characters which require no subset switching and can be entered directly.

Code 128B Data Field

The bar code symbol uses a series of varying width bars and spaces to represent an extensive character set (96 ASCII characters and seven control characters). The bars and spaces vary in width from one through four modules. Each character consists of three bars and three spaces that total 11 modules.

Code 128C Data Field

The bar code symbol uses a series of varying width bars and spaces to represent 100 pairs of numeric digits (00 through 99) and 3 control characters. The bars and spaces vary in width from 1 through 4 modules. Each character consists of three bars and three spaces that total 11 modules.

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