Microcom 438 - Manual (Page 108)

Chapter 6 Downloadable Graphics
438 Operator’s Manual - 880052-0100 6-7
6.6 Graphic Image Data Format
The image data consists of a set of data structures and location offsets to those structures.
All data is stored in binary form. Multi-byte values are stored least-significant-byte first.
The method illustrated below allows graphic images to span 64KB memory segments.
When using graphics over 64KB, the printer will determine the number of 64KB slots
required to store the entire graphic and will split the large file into the correct number of
smaller files internally. The printer stores these smaller files sequentially in the slots
following the one specified in the appropriate load or save graphic command. Therefore,
before sending a graphic file that is 64KB or more (uncompressed size), make sure that the
specified font slot has enough following empty slots to store the file properly.
Graphics that are stored in multiple slots in this way may still be printed as if they are one
large graphic. In the label format, refer to the first slot (the one specified in the download
command) regardless of how many slots that may be required for large graphics. The
printer will automatically append the additional graphic files seamlessly without additional
user intervention.
(Word is a 16-bit value, Byte is an 8-bit value, and Label is a location within the file)
Label start: the beginning of the file
Word, Word, lookup_table_offset
distance in bytes from start to beginning of
lookup_table (4 bytes)
Word tallest_char
height of graphic image in dots
Word widest_char Width of graphic image in dots
Byte default_spacing
Default spacing, usually 0
Byte byte_width
Width of graphic image in bytes
Byte first_char
20 HEX
Byte last_char
20 HEX
Byte default_char 20 HEX
Label lookup_table
beginning of lookup table
Word char_offset [last_char-first_char]
an array of offsets, one for each character in
font. Each offset is the distance, in bytes, from
the start to the beginning of the corresponding
character’s data structure. The first word in this
array is the offset to the first character’s data;
the last word is the offset to the last character’s
data.
Label first_char_data
the beginning of the graphic image data
Word char_height
height of this character’s bitmap in dots