Printronix p300 Maintenance Manual page 34

2–5. Print State
–continued
b. Character Generation
–continued
A lowercase character matrix occupies the top nine horizontal dot rows, and the three bottom rows remain
blank for space between lines. Underlines are only printed in the ninth row.
In normal six lines per inch spacing there are 12 dot rows from the top of one character line to the top of the
next. Spacing of eight lines per inch has nine dot rows per character line, spacing of nine lines per inch has
eight dot rows per line, and spacing of ten lines per inch has seven dot rows per line.
Elongated characters are generated from the normal matrix by printing each dot row twice except for the
first and last rows. The elongated character dot pattern, including underline, is shown in Figure 2–8.
In normal character printing, dots are only printed in alternate dot columns in any dot row. The matrix for
an addressed character is read out one row at a time by the binary row count RC1 through RC4. For every
dot row, the character code is recirculated and a dot can appear in any of the twelve dot columns.
Because the PROMs provide only eight outputs, the encoded PROM output line must be read twice. Bits
on the eight lines are multiplexed one line at a time over the COM line to the hammer driver PCBA. Multi-
plexing is under control of the dot column counter output DC1–DC4. COM is then clocked into the ham-
mer driver logic.
During the SYNC period, information appearing at the hammer driver logic for every character read from
the printer buffer consists of a "1" bit (dot) or a "0" bit (no dot) for each specific dot column and row. On the
P300, only every third bit (representing every hammer location) in the COM data stream is clocked into
the hammer driver shift register so that the 44 (132/3) hammer driver circuits may be pulsed. On the P600,
only every second bit (representing every second character location) in the COM data stream is clocked
into the hammer driver shift register so that the 66 (132/2) hammer driver circuits may be pulsed.
2–12 P300/P600 Principles of Operation