DFX-8500
Figure 2-16 shows the data flow for data input via the parallel interface. Although various circuits perform data processing, the control core is the CPU and all operations are executed via the CPU. 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 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 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 printhead data.
Note : The data flow from the
E05B36 (IC1) | CPU (IC2) |
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/STROBE |
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| Input Data Buffer |
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1 | STBINT | 2 |
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DATA | DATA | CR command ? | DATA | Buffer full ? |
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| Yes |
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BUSY, /ACK |
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3 |
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| MMIO |
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| CPU (IC2) |
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| 4 |
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| Command |
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| Analyzer |
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| Line Buffer | 5 |
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| Attribute |
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| Character Gnerator | Image Buffer | |
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| Controls |
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| printer mechanism. |
| Down Load |
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8 | 6 |
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E05B36 7
Figure 2-16. Parallel Interface Data Flow
Rev. B |
