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Figure 9-12. These download characters are defined as proportional
characters.
attribute byte, mO. As you know, the first bit of m0 is used to
specify whether the character is a descender or not. The next
three bits are used to specify the starting print column (acceptable
values are 0 to 7). The last four bits specify the ending print column
(acceptable values are 4 to 11). The minimum character width
is five dots (so you could not, for instance, specify a starting
column of 6 and an ending column of 8, even though those are
both within the acceptable range). If you inadvertantly give an
incorrect width value, however, SD-lo/15 is forgiving: it will
automatically revert to the default width of eleven dot columns.
Just as there was an easy trick for figuring the attribute byte
earlier, you still don’t need to know a thing about binary
arithmetic. Merely multiply the starting column by 16, add the
ending column number, and add 128 if the character is not a
descender. If you prefer a formula: (descender * 128) + (start
* 16) + end.
The examples in Figure 9-12 show characters of different
widths. These characters are defined in the program’below; the
output is shown in Figure 9-13.
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