Printronix p300 Maintenance Manual page 40

2–5. Print State
–continued
c. Character Generation Logic
As subsequent SYNC pulses are generated by timing disk rotation, outputs of the SYNC counter appear at
the three following PROM devices:
–Dot Column Count PROM – decodes counts to provide the dot column count (DC1–DC4).
–Character Column Count PROM – decodes counts for the character column count and NTA for the
A4 and A6 logic boards.
–Control Decode PROM – decodes various counts which generate control signals NSPT, NSPFP,
NEMOV (P600 only), and NTA for A7 or later logic boards only. This PROM functions during
all three states of operation of the printer.
The character column count PROM encodes a binary count every 12th SYNC pulse that defines the char-
acter columns. The PROM repeats the process for two (or three) character columns followed by an addi-
tional count of 14 (or ten) pulses for shuttle turn around at the right end of shuttle travel. As the shuttle
moves left, the two groups of 12 pulses are repeated followed by a count of turnaround SYNC pulses and a
RESYNC for left end turnaround. This completes the shuttle cycle.
The character column count PROM provides outputs CC1–CC3 and the turn around signal NTA. The bi-
nary count generates hammer shift clock pulses, NHSC, for each one of the SYNC periods (36 for P300;
24 for P600) during which printing occurs.
Hammer shift clock, HSC, counter logic is a count of two (three for P300) counters clocked by SRCLK. Its
output appears at a comparator which asserts its "equals" output only under the following two conditions:
–A modulo three (or two) numbered character is read from the printer buffer and the bits CC1–CC2 are
encoded to match the group of 12 pulses.
–Bits CC1–CC2 are not encoded at a turnaround.
The hammer bank shift register is clocked by NHSC (gated SRCLK pulses) and loaded with data corre-
lated to the character position.
The signal TAI is generated to inhibit any NHSC pulses during turnaround periods. TAI is synchronized
with the SYNC and CLKB pulses. This provides the signal NTA which controls the NHSC gate.
Three other control signals are generated by the control decode:
–Start print, NSPT, initiates the print state in state control logic.
–Start paper feed pulse, NSPFP, increments the dot row counter.
–Early move, NEMOV (P600 only), occurs with NSPFP (at either end of the shuttle travel) and initi-
ates paper movement to the next dot row during the print state.
2–18
–continued
P300/P600 Principles of Operation