Epson DFX-8500 Service Manual page 73

DFX-8500
Figure 2-16 shows the data flow through the parallel interface. Although various circuits perform data
processing, the control core is the CPU, where all operations are executed. In this circuit, the E05B36 IC
(IC1) provides the interface between the external host computer and the CPU, and all data processing is
performed by read/write operations to MMIO (Memory Mapped Input/Output).
Data from the host computer is accepted and stored (latched) by repeating steps 1 through 3 below.
1. Upon receiving the /STROBE pulse, IC1 latches the data into ports PDATA 1 - 8 and sets the BUSY
signal to HIGH.
2. The CPU reads the latched data from the MMIO 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 IC1 clear the BUSY signal and output the /ACKNLG signal, via
the MMIO accesses. When either a CR code is received or the input data buffer becomes full, the CPU
sets the BUSY signal to HIGH and executes printing.
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 1-byte character codes
and 2-byte attributes. Character data is stored as character codes and commands or character types are
stored as attributes.
5. The print data is stored in the line buffer in units of one line of data.
6. The CPU reads the print data stored in the line buffer byte by byte, accesses the CG (Character
Generator), and turns the ASCII data into dots in the image buffer (or in the case of downloaded
characters, in the download CG). A row of dots is output to the printhead control circuit as printhead data.
Note: The data flow from the Type-B I/F card is the same as the data flow from the parallel interface,
described above, except the signal names and data access method differ.
/STROBE
DATA
BUSY, /ACK
3
2-20
E05B36 (IC1) CPU (IC2)
1 2
STBINT
CR command ?
DATA
MMIO
CPU (IC2)
Command
Analyzer
Attribute
Controls
printer mechanism.
Figure 2-16. Parallel Interface Data Flow
RAM (IC3)
Input Data Buffer
No
Buffer full ?
DATA
Yes
Yes
4
Line Buffer 5
Character Generator
Download
6
8
E05B36
Image Buffer
7