Epson DFX-5000+, Service Manual

Page: 75 / 223

Operating Principles
Data from the host computer is latched by repeating steps 1 through 3 below.
1. Upon receiving the STROBE signal, IC7 latches the data into ports DIOO 7
and sets the BUSY signal to HIGH.
2. The CPU reads the latched data from the port, checks whether the data
is a print command (CR code), and stores it in the input data buffer if it is not.
3. After checking the data, the CPU makes IC7 clear the BUSY signal and output
the ACKNLG signal, via the
accesses. When either a CR code is
received or the input data buffer becomes the CPU sets the BUSY signal
to HIGH and executes printing.
Figure 2-19. Data Flow from the Parallel Interface
4. The CPU reads the data from the input data buffer, analyzes each byte to
determine whether it is a character or a command, and converts it to print
data. The print data consists of l-byte character codes and 2-byte attributes.
Character data is stored as character codes and commands or character types
are stored as attributes.
EPSON Service Manual
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