The FCB data following the header information is a series of 1-byte line control codes for each physical line of the form. There are 18 to 144 of these bytes, depending on the length of the form.

Each byte is a bit pattern describing one of 12 channel codes for vertical forms positioning and one of four lines-per-inch codes for vertical line spacing. The structure of the 3800 FCB module is shown in Figure 1.

Figure 1. 3800 FCB Module Structure

• The top and bottom 1/2 inch of each page are unprintable, and the bytes corresponding to these positions must be void of any channel codes. Three bytes of binary zeros are supplied by the IEBIMAGE utility for the top and bottom 1/2 inch.
• The total number of lines defined in the module must be equal to the length of the form. The printable lines defined must start 1/2 inch below the top and stop 1/2 inch from the bottom of the form.