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Bits 11–4 (Character Code): These 8 bits define which of the 254 characters is to be called from the character ROM. Valid

character codes are 0x02–0xFF.

Bits 3–0 (Attribute Code): These 4 bits address the attribute table used to specify which of the 16 locations in RAM specify the

colors and enhanced features to be used for this particular character. Two separate attribute tables are used, one for 2-color

characters, the other for 4-color characters.

Each of the characters are stored in sequence in the page RAM. Special codes are used between lines to show where one line

ends and the next begins, and also to allow blank (or ‘skipped’) single scan lines to be added between character rows.

ROW END CODE

To signify the end of a row of characters, a special Row-End (RE) code is used in place of a character code.

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Bits 11–4 (Row-End Code): A special character code of 0x01

Bits 3–0 (Don’t care)

The RE character tells the OSD generator that the character codes following must be placed on a new row in the displayed

window.

SKIPPED LINE CODE

Each displayed row of characters may have up to 15 skipped (i.e., blank) lines beneath it in order to allow finer control of the

vertical spacing of character rows. (Each skipped line is treated as a single auto-height character pixel line, so multiple scan lines

may actually be displayed in order to maintain accurate size relative to the character cell — see section Constant Character

Height Mechanism). To specify the number of skipped lines, the first character in each new row of characters to be displayed is

interpreted differently than the other characters in the row. Instead of interpreting the data in the location as a character code, the

12 bits are defined as follows:

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Bits 11–8 (Reserved): These should be set to zero.

Bits 7–4 (Skipped Lines): These four bits determine how many blank pixel lines will be inserted between the present row of

display characters and the next row of display characters. A range of 0–15 may be selected.

Bits 3–0 (Attribute Code): The pixels in the skipped lines will normally be Color 1 of the addressed 2-Color Attribute Table entry.

Note that the pixels in the first line immediately below the character may be overwritten by the pixel override system that creates

the button box. (Refer to the Box Formation Section for more information).

Each new line MUST start with an SL code, even if the number of skipped lines to follow is zero. An SL code MUST always follow

an RE control code. An RE code may follow an SL code if several ‘transparent’ lines are required between sections of the window

(see example 3 below). In this case, skipped lines of zero characters are displayed, causing a break in the window.

WINDOW END CODE

To signify the end of the window, a special Window-End (WE) code is used in place of a Row-End code.

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Bits 11–4 (Row-End Code): A special character code of 0x00.

Bits 3–0 (Don’t care)

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