Printronix p300 Maintenance Manual page 69

2–6. Paper Feed State
h. Channel Seek Operation (Figure 2–29 through Figure 2–32)
Channel seek operations locate specific lines on a form. A channel seek operation occurs when the follow-
ing conditions exist:
–The channel number code is entered on data lines DB1 through DB7 as a terminator for a line of print.
–The required channel number has been loaded in the EVFU memory.
–The internal paper instruction line is active. PI can be either a decoded word from the program or the
logic line from a Dataproducts interface. The resulting NSPI signal loads the four bit code into
the data latches and sets the vertical format slew signal VFS which causes paper feed logic to start
paper movement as a form feed operation.
As paper advances through each line space, the row count recycles, generating a delayed line clock,
NDLC, which appears at the VSC line. As a result, the contents of the EVFU memory are stepped one
address position for each line of paper feed. The contents then appear at a comparator.
When the output of the EVFU memory matches the number in the data latches, both the data latches and
the VFU flip–flop are reset, stopping paper movement and ending the EVFU sequence.
Every time the EVFU memory is incremented, the memory address counter is incremented. When the
count in the memory address counter equals that in the forms length counter, the memory address counter
is reset.
The VFS signal generated by the EVFU configures the logic to generate the velocity profile for a channel
seek operation.
i. Vertical Tab Operation
The EVFU may be operated by a programmed VT code OB
ory has been loaded, a search is begun for channel 12 code. The EVFU slews paper until channel 12 code is
found in the EVFU memory. If the EVFU memory has not been loaded, a single line feed results.
j. Binary Count Operation (Figure 2–33)
In the binary count operation, the program may request that paper be slewed a specified number of lines
(one to 16) from the current position. Although this function is controlled by the EVFU, it is not necessary
that the EVFU be loaded.
Conditions for this mode of operation are as follows:
–The PI line from the host system is active and jumper W5 is absent.
–Data bit DB5 is high to generate binary count, BC.
–Data bits DB1 through DB4 encode the number of lines to be slewed.
P300/P600 Principles of Operation
–continued
H
, which generates vertical tab NDVT. If mem-
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