Printronix p300 Maintenance Manual page 63

2–6. Paper Feed State
–continued
d. Skip–Over Perforation (Figure 2–26)
The row counter in top–of–form logic always counts up to 792 rows (11 x 72) for an 11 inch form. The
count refers to the physical top–of–form, provided the paper supply is set properly and not changed.
The printer may be configured to skip over perforations so that printing ends before the bottom of the form
and resumes at the top of the next form.
Selectable skip–over distances –– 1/2", 2/3", 5/6", and 1" –– will be precise for a given configuration re-
gardless of printer line space setting.
The skip–over distance is selected by installing jumpers W1, W2, and W3 on the logic B PCBA. Refer to
the User's Reference Manual for instructions on skip–over perforation length select.
e. Paper Feed to Top–of–Form (Figure 2–26 through Figure 2–28)
The top of form logic maintains an accumulated count of dot rows and lines printed since the start of print-
ing. If a top of form command is received, this logic controls the high speed movement of paper to the top
of the next form.
The top of form command originates either at the TOP OF FORM switch with signal STOF or at the printer
command decoder with signal NDFMFD. The resulting NTOF signal sets the FMFD flip–flop in top of
form logic. As NFMFD goes through, it generates the slew signal NSLW that holds off the EPFP pulse and
modifies the address applied to the velocity PROM in the paper feed velocity counter logic. Velocity
counter logic then generates pulses at a rate that drives paper briefly at seven inches per second on the P600
(five inches per second on the P300). The step counter and velocity counter in the velocity counter logic
then cause paper movement to accelerate in stages up to approximately 15.5 inches per second during the
next 12 row counts on the P600 (8.5 inches per second for the P300). That velocity is maintained until the
beginning of the last line of the form FLL is detected. FLL causes the velocity PROM and velocity counter
logic to generate paper feed pulses at a lower rate until paper movement stops following the last line of the
form.
Two counters in the top of form logic keep a count in RCLK pulses of dot rows from the top of one form to
the top of the next. The final RCLK pulse increments the line counter to 66, clearing the line counter so that
it is ready to begin the next form. Twelve rows prior to the end of a form, FLL is generated from the top of
form PROM, which modifies the velocity PROM address, clocks end form feed, NEFF, and resets the
FMFD flip–flop, turning off NSLW. NEFF simulates the final row count and sets RCR, which produces
EPFP. EPFP resets the PPF flip–flop to end the paper feed state and initiate the buffer load state.
P300/P600 Principles of Operation 2–41