A&D 191 User Manual

Page 25

The mechanism used in the printer prints one line of dots
across at a time. This means that when it prints one line
of characters it has actually printed ten lines of dots
where the first eight lines make up the character and the
last two lines are blank for the space between character
lines. By using the CHR$(18) control code, you can tell the
printer which dots to print for one whole dot line. Since
there are 144 dots per line, you must follow the CHR$(18)
control code with 144 bits of information. For every place
there is a one in the 144 bit pattern you send, the printer
will print a dot. Rather than receive one bit at a time the
printer expects to receive the information eight bits at a
time. This means that after receiving a CHR$(18) the next
eighteen 8 bit characters it receives will be printed as
dots to form one dot line.

To figure out the dot pattern values to send after the
CHR$(18), you will need some grid paper. A large sheet
with 144 grid boxes across would be convenient. If such a
large sheet of paper is not available, you could divide your
pattern in half and work with 72 grid boxes across. Divide
up your grid paper by drawing a heavy line down every 8
boxes across. Now fill in each box of the grid that you
want to be printed. Now do the following procedure to
compute the eighteen values which describe your desired
bit pattern.

Imagine placing the number sequence over each of the
first eight grid boxes.

Now add together all the numbers above the boxes
which are filled in or have a dot as in the example above.
In our example, we would have 2 + 16 + 32 which
equals 50. ‘50’ then would be the first entry of a data
statement which would be followed by seventeen more
numbers computed in the exact same manner as the
example.
Once you have the eighteen values in a data statement,
you need simply run a program which prints a CHR$(18)
followed by the data value read from the data statement.
Don’t forget to end all of your print statements with
semicolon. This will prevent carriage returns CHR$(13)
from being sent, which would become part of the
eighteen data values for which the printer is waiting.

Dot Graphics

Code 18

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