Plotting The Six Bit Code - Printronix p300 Maintenance Manual

2–5. Print State
–continued
d. Dot Row Counter Logic (Figure 2–11)
Dot row counter logic on the logic B PCBA generates a four bit binary count, RC1–RC4, which causes the
PROM output to define each row of dots in the entire character line, including the space between lines.
When print state is entered, characters are read from the buffer and the row counter is incremented by start
paper feed pulses, SPFP.
Row counter reset, RCR, resets the row counter at 12 pulses for six lines per inch or nine pulses for eight
lines per inch. The subsequent even paper pulse, EPP, resets RCR. The actual character normally consists
of seven dot rows. If NPAL is true, however, a nine dot row character is printed. NPAL is derived from the
underline signal, SDUL, or from a print nine rows flag from the PROM decoder; either signal allows for
dot data in these rows.
When the last row in the character has been printed, counter logic provides an EOP signal, terminating the
print state and entering the paper feed state which advances the paper to the top of the next character field.
EOP also sets the paper feed mode, PPF, and the row counter is subsequently clocked at an increased rate
until the row count produces end of paper motion (EPFP).
When printing elongated characters, the decoded elongated character, NDELC, signal increments the row
counter with every second RCLK, either SPFP or NOPP. This causes each row of dots in the character
(except the first and last rows) to be printed twice.
In plot mode operation, each line of data specifies dots to be printed in a single dot row. The PM signal
(instead of the decoded row count) enables the SPFP pulse to generate end of print (EOP) which implies a
new buffer load cycle is required.
Figure 2–11. Plotting the Six Bit Code
P300/P600 Principles of Operation 2–19