Printronix p300 Maintenance Manual page 67

2–6. Paper Feed State
f. Electronic Vertical Format Unit
The electronic vertical format unit (EVFU) is a software controlled vertical formatter. It is loaded and op-
erated by the host computer without operator intervention. When the EVFU is loaded, it disables perfora-
tion skip over and default forms length.
For the RS 232 interface, DB8 (MSB) can be jumpered to assert PI when it is required. When used in this
way, alternate character set can not be selected by DB8 (MSB); instead, alternate characters may be se-
lected by control codes hex 0E and hex OF.
For systems that do not provide PI signal control at the interface, a program protocol may be used to per-
form the load function. The protocol is:
–Jumper W5 on the logic A PCBA must be installed.
–Data bit DB5 must be high.
–Data bits DB6 and DB7 must be low.
Note that binary count operation is not available under the above conditions.
The EVFU can be disabled by connecting jumper W7 on the logic B PCBA. Jumper W7 disables the paper
instruction strobe, NSPI, so that the EVFU cannot operate.
Use of the EVFU to define print positions on a form increases system efficiency by allowing the printer to
slew paper to a predetermined line with a single command. Three modes of EVFU operation are available:
–Programming the EVFU memory
–Slewing to a specified line
–Slewing a specified number of lines
g. Programming EVFU Memory (Figure 2–29 and Figure 2–30)
The EVFU memory is a four bit RAM that stores up to 132 channel codes, each numbered within a range of
channel 1 to channel 14. EVFU program information is transmitted to the printer on interface data lines
DB1 through DB7. The data is loaded into the interface data latches and then into the EVFU by NSPI. The
memory is programmed in three steps:
–A start load command, NSTL, is sent over the interface data lines, decoded, and sets the EVFU load
flip–flop. The flip–flop is clocked by paper instruction strobe, NSPI, DSTB, and PI. This combi-
nation asserts load EVFU (LD). LD initializes EVFU control logic and enables the EVFU mem-
ory to be loaded.
–The EVFU channel codes follow the Start Load command. With the memory initialized by the pre-
vious code, each channel code loads sequentially in ascending memory address locations in the
order received. Each code is accompanied by a paper strobe (NSPI), which steers the data bits
DB1 through DB4 to the EVFU memory. At the same time, the memory address counter and the
forms length counter are incremented. This process is repeated until the last channel command
has been loaded.
–After the last channel command has been loaded, an end load command is decoded and sent to the
load flip–flop. The flip–flop is clocked by NSPI and resets. The EVFU memory is disabled from
further loading. The forms length counter stops incrementing immediately, but the EVFU
memory accepts the ELD code.
P300/P600 Principles of Operation
–continued
2–45