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Chapter 15 Bi-Tronics Parallel Interface
Bi-Tronics Parallel Interface
Bi-Tronics is a parallel interface with bidirectional c apabilities. Features
include the following:
•Timing of the signals has been reduced, thereby speeding dat a
transmission.
•Bidirectional communication. Both the host and the printer can send da ta.
•Versatility. If a device cannot send data along parti cular lines, the Bi-
Tronics interface can send data via other operating modes, s uch 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 error s. For example,
instead of having to physically check if the printer ha s run out of paper,
you can create a program to query this from the host. The pr inter will
respond and a message will display on the host.

Operating Modes

The Bi-Tronics interface supports three operating modes, whic h are
determined by negotiation between the printer and the host.

Compatibility Mode

This mode provides compatibility with Centronics-like ho st I/O. Data is
transferred from the host to the printer in 8-bit bytes over the da ta lines.
Compatibility mode can be combined with nibble and byte mo des 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 b ypass this,
the Bi-Tronics interface permits data to be sent as hal f a byte over four status
lines. (Half a byte equals one nibble.) Two seq uential four-bit nibbles are sent
over the lines.
Data is transferred from printer to host in four-bit nib bles over the status lines,
and the host controls the transmission.

Byte Mode

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