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After the data is stored, the MPU accesses the data to
find, from the formatting control codes within the data,
what is to be done. Lines to be printed are formatted
and placed in 1 of the 2 print buffers (up to 132
characters each). Control then passes to the printer
control routine which addresses the character locations
in the character generator to fire the print wires. No
formatting is allowed until the print buffer in use is
empty (at least 1 line is printed). However, at least once
each 25 milliseconds, control transfers to the
cable-handler routine that services write data commands
and provides addresses for buffer space.
During printer operation the MPU services the printer
interface registers, as needed, to keep the printer
operating.
A print routine contains microcode that handles the
recognition of print buffer contents, determines in which
direction and how far the print head is to move, and
controls line feeding, print head motion, starting, and
stopping.
4-4
The M PU uses the print routine to recognize the starting
point of the print line. The MPU determines how far
and in what direction the print head must move from its
present location. The MPU also determines if the next
line to be printed requires a stop, high-speed tab,
normal-speed tab, and whether the line feeds can be
completed without stopping the print head.
While the wires are firing, the print routine handles
loading of the address for the next group of wires to be
fired from the character generator.
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