Lexmark 249X, 248X manual Managing the Download Area, 124, Lookup Table

Bit	Bit Values	Functions
5-9		Used for the compression mask. There is
		one bit per dot column with bit 7 of byte 5
		mapping to the leftmost column. For a
		character with 36 dot columns when
		decompressed, bit 4 of byte 9 would map to
		the rightmost column.
		All zeros indicate that a character is not
		compressed.
		If a proportional character has more dot
		columns than compression mask bits, the
		remaining dot columns must be stored
		without compression.
		Only 39 dot columns can be compressed.
		Bit 40 of the compression mask is reserved.

The Lookup Table

•ASCII character 255, xFF, cannot be defined. It is a mandatory space and is the same size as ASCII character 32, x20.

•ASCII Character 0, x00, is the zero slash. Any character downloaded to 0, x00 replaces the zero. If the zero slash is selected from the operator panel, the download character is printed instead of ASCII character 48, x30.

•All block graphic characters are 30 dots high, even though only 24 dots are defined for each column.

An underscore character is defined as a blank-block graphic character (all zeros). The underscore is generated by the printer during the second pass.

A shading-block graphic character repeats dots 1-6 of each column as dots 25 through 30, respectively.

A line-drawing-block graphic character repeats dots 23 and 24 as the pairs 25/26, 27/28, and 29/30.

•An entry can point to any character data image whether resident or down- loaded. Multiple entries can point to the same image. The address of an undefined entry should be zero. An undefined entry is printed as a space.

Managing the Download Area

If you are downloading and know the status of preceding downloaded information, you should not have any conflicts in character management. If, however, there is previously downloaded information in the download area and you are not sure of its status, you can write over the download area with the resident lookup tables for the currently selected code page. To write over any existing download data, send the printer command ESC = 0 0. Sending ESC = 0 0 clears the existing download data and copies the resident lookup tables to the download area.

124 Section 7: Downloading Characters and Fonts