7.4.1. Hardware Setup

This section tells about the various ways you can connect a printer to your PC. It talks about the kinds of ports and cables, and also the kernel configuration you may need to enable FreeBSD to speak to the printer.

If you've already connected your printer and have successfully printed with it under another operating system, you can probably skip to section Software Setup .

7.4.1.1. Ports and Cables

Nearly all printers you can get for a PC today support one or both of the following interfaces:

• Serial interfaces use a serial port on your computer to send data to the printer. Serial interfaces are common in the computer industry and cables are readily available and also easy to construct. Serial interfaces sometimes need special cables and might require you to configure somewhat complex communications options.

• Parallel interfaces use a parallel port on your computer to send data to the printer. Parallel interfaces are common in the PC market. Cables are readily available but more difficult to construct by hand. There are usually no communications options with parallel interfaces, making their configuration exceedingly simple.

  Parallel interfaces are sometimes known as ``Centronics'' interfaces, named after the connector type on the printer.

In general, serial interfaces are slower than parallel interfaces. Parallel interfaces usually offer just one-way communication (computer to printer) while serial gives you two-way. Many newer parallel ports can also receive data from the printer, but only few printers need to send data back to the computer. And FreeBSD doesn't support two-way parallel communication yet.

Usually, the only time you need two-way communication with the printer is if the printer speaks PostScript. PostScript printers can be very verbose. In fact, PostScript jobs are actually programs sent to the printer; they needn't produce paper at all and may return results directly to the computer. PostScript also uses two-way communication to tell the computer about problems, such as errors in the PostScript program or paper jams. Your users may be appreciative of such information. Furthermore, the best way to do effective accounting with a PostScript printer requires two-way communication: you ask the printer for its page count (how many pages it's printed in its lifetime), then send the user's job, then ask again for its page count. Subtract the two values and you know how much paper to charge the user.

So, which interface should you use?

• If you need two-way communication, use a serial port. FreeBSD does not yet support two-way communication over a parallel port.

• If you don't need two-way communication and can pick parallel or serial, prefer the parallel interface. It keeps a serial port free for other peripherals---such as a terminal or a modem---and is faster most of the time. It's also easier to configure.

• Finally, use whatever works.

7.4.1.2. Parallel Ports

To hook up a printer using a parallel interface, connect the Centronics cable between the printer and the computer. The instructions that came with the printer, the computer, or both should give you complete guidance.

Remember which parallel port you used on the computer. The first parallel port is /dev/lpt0 to FreeBSD; the second is /dev/lpt1, and so on.

7.4.1.3. Serial Ports

To hook up a printer using a serial interface, connect the proper serial cable between the printer and the computer. The instructions that came with the printer, the computer, or both should give you complete guidance.

If you're unsure what the ``proper serial cable'' is, you may wish to try one of the following alternatives:

• A modem cable connects each pin of the connector on one end of the cable straight through to its corresponding pin of the connector on the other end. This type of cable is also known as a DTE-to-DCE cable.

• A null-modem cable connects some pins straight through, swaps others (send data to receive data, for example), and shorts some internally in each connector hood. This type of cable is also known as a DTE-to-DTE cable.

• A serial printer cable, required for some unusual printers, is like the null modem cable, but sends some signals to their counterparts instead of being internally shorted.

You should also set up the communications parameters for the printer, usually through front-panel controls or DIP switches on the printer. Choose the highest bps (bits per second, sometimes baud rate) rate that both your computer and the printer can support. Choose 7 or 8 data bits; none, even, or odd parity; and 1 or 2 stop bits. Also choose a flow control protocol: either none, or XON/XOFF (also known as in-band or software) flow control. Remember these settings for the software configuration that follows.