Epson DFX-5000+, Service Manual

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Operating Principles
5.
6.
7.
8.
The print data is stored in the line buffer in units of one line of data.
The CPU reads the print data stored in the line buffer byte by byte, accesses
the CG (Character Generator), and expands the data in the image buffer (in
the case of download characters, in the download CG). A row of expanded data
is output to the printhead control circuit as head data.
When data is expanded to an italic or super/subscript character, the CPU uses
IC7 to expand it via MMIO.
The CPU controls the CR motor by calculating the control data for each line
from the print data in the line buffer. When a paper feed command is sent
after one line is printed, the CPU executes paper feeding.
For NLQ characters, printing one line consists passes; the printer performs
steps 6 through 8 twice. When the CPU expands the data from the CG in the
image buffer, it uses the 24-bit shift register in IC7. The CPU is always ready to
fetch data so printing can be viewed as an interrupt-to-fetch operation. Whenever
the input data buffer is not full between printing operations, data is fetched. Table
2-3 describes the functions main printer components.
Note :
The data flow from the serial interface is the same as the data flow from the
parallel interface, described above, except the signal names and data access
method differ.
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EPSON DFX-5000+ Service Manual