Chapter 5 IEEE 1284 Parallel Interface
IEEE 1284 Parallel Interface
The IEEE 1284 is a parallel interface with bidirectional capabilities. Features include the following:
•Timing of the signals has been reduced, therefore speeding data transmission.
•Bidirectional communication. Both the host and the printer can send data.
•Versatility. If a device can not send data along particular lines, the 1284 can 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
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
Data is transferred from printer to host in
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.
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