Centronics Parallel Interface Signals; Ieee 1284 Parallel Interface; Compatibility Mode; Nibble Mode - Printronix P8000 Series Administrator's Manual

Centronics Parallel Interface Signals

Data Lines 1 through 8. Provides eight standard or inverted levels from the host that specify character
data, plot data, or a control code. Data Line 8 allows access to the extended ASCII character set. You
may enable or disable this line via the Data Bit 8 parameter on the Centronics submenu (see page 81).
Data Strobe. Carries a low true, 100 ns minimum pulse from the host that clocks data into the printer.
Acknowledge. A low true pulse from the printer indicating the character or function code has been
received and the printer is ready for the next data transfer.
Online. A high true level from the printer to indicate the printer is ready for data transfer and the ONLINE
key on the control panel has been activated. When the printer is in online mode, it may accept data from
the host.
Paper Empty (PE). A high true level from the printer to indicate the printer is in a paper empty or paper
jam fault.
Busy. A high true level from the printer to indicate the printer cannot receive data.
Prime. A high true level from the host to indicate the printer should perform a warm start (printer is reset
to the power-up configuration values).
Paper Instruction (PI). Carries a CVFU signal from the host with the same timing and polarity as the data
line.
Fault. A low true level from the printer indicates a printer fault.

IEEE 1284 Parallel Interface

The 1284 supports three operating modes, which are determined by negotiation between the printer and
the host.

Compatibility Mode

This mode provides compatibility with Centronics-like host I/O (see Table 18). Data is transferred from the
host to the printer in 8-bit bytes over the data lines.
Compatibility Mode can be combined with Nibble and Byte Modes to provide bidirectional communication.

Nibble Mode

Eight bits equals one byte. When a byte of data is sent to the printer, the eight bits are sent over eight
data lines.
Some devices cannot send data over their eight data lines. To bypass this, the 1284 permits data to be
sent as half a byte over four status lines. (Half a byte equals one nibble.) Two sequential four-bit nibbles
are sent over the lines.
Data is transferred from printer to host in four-bit nibbles over the status lines, and the host controls the
transmission.

Byte Mode

The printer and host send data to each other along eight data lines (one bit per line).
If bidirectional communication is supported by the printer and the host, the host will take control of the
data transfer.

Signals

Table 18 lists each of the signals associated with the corresponding pins on the 1284 interface.
Descriptions of the signals follow.
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