IBM 6400 Series, Setup Manual

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Chapter 5
IEEE 1284 Parallel Interface
Some application programs require a unique configuration. If the printer is not
working properly in the configuration you have selected, contact an IBM
service representative.
IEEE 1284 Parallel Interface
The IEEE 1284 is a parallel interface with bidirectional capabilities. Features
include the following:
Faster data transmission. Timing of the signals has been reduced.
Bidirectional communication. Both the host and the printer can send data.
Versatility. If a device cannot send data along particular lines, the 1284 can
work around this and send data via other operating modes, such as Nibble
Mode which is discussed later.
Less user interaction. The host can ask the printer about printing status and
supported features, such as fonts and internal errors. For example, instead of
having to physically check if the printer has run out of paper, you can create a
program to query this from the host. The printer will respond and a message
will display on the host.
Operating Modes
The 1284 supports three operating modes, which are determined by
negotiation between the printer and the host.
Compatibility Mode
This mode provides compatibility with a Centronics or PC Parallel interface
(see Table 9). 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.