Epson LQ-2550 Technical Manual page 95

REV.-A
I n t e r f a c e
2.3.2
This printer has both an 8-bit parallel interface and an RS-232C serial interface.
2.3.2.1 8-Bit Parallel Interface
Operating Principles
Figure 2-42 shows the 8-bit parallel interface data transmission timing. Data is transferred between
a host computer and the printer using the following sequence:
BUSY
DATA
STROBE
a) First, the host computer confirms that the BUSY signal from the printer is low or that the ACKNLG
signal from the printer is high. When the BUSY signal is low, the printer is ready to receive data.
When it is high, the printer can not receive data from the host computer since the printer is
data. Therefore, the host computer does not transfer data until the BUSY signal changes
from high to low. (Some host computers check both the BUSY and ACKNLG signals, and others just
check either the BUSY or ACKNLG signal.)
b) After the host computer has confirmed that the BUSY signal is low, it places data (8 bits per word)
in parallel on the data bus (DO - D7), and the printer reads the data atthefalling edge of the STROBE
pulse.
c) After receiving a data word from the host computer, the printer sets the BUSY signal high to inform
the host computer that the printer is proseccing
After proseccing the data, the printer sets the ACKNLG signal low, allowing the host computer to
d)
transfer data again. The printer sets the BUSY signal low approximately 5 ps after setting the
host computer that the printer is ready to receive data.
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Figure 2-42. 8-Bit Parallel Data Transmission Timing
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data and is not ready to receive any more data.
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