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Now we will calculate the vertical numerical values of the columns of dots,
and enter themunderneath thegrid. Each verticalcolumn isfirstdivided into
three groups of eight dots. Each group of eight dots is represented by one
byte. which consists of eight bits.
This is where the numbers down the left side of the grid come in. Notice that
there is a number for each row of dots and that each number is twice the
number below it. By making these numbers powers of two we can take any
combination of dots in a vertical column and assign them a unique value.
Assigning the Index Table data
Unlike defining inthe Standard mode, you must assign theIndex Table with
the IBM mode. This Index Table is prepared for the information of each
characters attribute data, such ascharacter type (Normal 24-dot high, or 30-
dot high block graphics), the dot pattern data in the memory, and the
compression mask bit data.
Each character requires 9 index table data.
The first and the second bytes (m] and m2) indicates theposition of the first
dot pattern in the memory.
ml isthe high order byte. and m2 isthe low order
byte.
The third byte,m3,indicates thecharacter typeand the dot pattern data width
in the memory.
If the character is normal. simply enter the width of dot pattern in the
memory. If the character is a block graphic. add 128 to the width of dot
pattern in the memory.
Our telephone symbol isa normal character and the width of the dot pattern
in the memory should be 25, so this value is 25.
The fourth byte,
m4, indicates the printing attribute.
This byte indicates the character width to be printed, and information of the
repetition dots for block graphics characters.
If the character is a normal character, add 192to the character width.
If the character is a block character, and it should be printed as a line draw
character, add 64 to the character width. If the block character is not a line
draw character, this byte should be the same as the character width.
Our telephone symbol isanormalpicacharacter. sothe
character width is 35,
and this byte should be 227.
129