Tutorial 12

Impact printers produce an image on paper by physically striking an inked ribbon against the surface of the paper. The advantages of impact printers are that they tend to be inexpensive and print at a relatively high speed. Impact printers were very popular in the late 1980s. Some disadvantages of impact printers are lower print quality and noise.

Ink-jet printers have replaced dot-matrix printers at the low end of the market. Many computer manufacturers and large computer stores offer ink-jet printers along with computers as part of package deals. They produce good-quality printing and are relatively fast, while requiring little maintenance beyond replacing the cartridge. What makes them attractive is their ability to easily produce color, as well as standard black-and-white images. High-quality color ink-jet printers are available; however, high-quality color printing comes at a cost. It requires a good printer and special paper that will prevent "wicking" of the ink, which causes a fuzzy appearance.

Laser printers have become one of the most popular types of printer for home use and are a must for most office environments. They produce high-quality, high-speed printing. Early laser printers were notorious for generating lots of heat and consuming lots of power.

A dot-matrix printer is an impact printer. Its main advantages are its ability to print forms (multiple pages) and its high reliability and low operating cost. Its disadvantages are its noise, slow speed, and generally low-quality (by today's standards) images.

1. Clean the drum.
2. Charge the drum.
3. Write the image.
4. Transfer the toner.
5. Transfer the image.
6. Fuse the image.

Many of a laser printer's critical components, including those that experience the most wear and tear, are incorporated into the toner cartridge. The most important is the photosensitive drum. By incorporating these components into the toner cartridge, chances of failure are reduced because the primary-wear components are constantly replaced.

If residual particles remain on the drum, they will appear as random black spots and streaks on the next printed page. The drum will need to be cleaned to clear this problem.

There is a vast array of printers available and in order to ensure that you are obtaining optimum performance, the printer, the printer driver, and the software using the printer must be configured for the same mode. The IEEE 1284 standard establishes the standards to ensure printer compatibility.

Computers transfer data by means of parallel wires or buses. Computer modems use serial communication. Telephone systems use only two wires.

A modem is a peripheral device that enables computers to communicate with each other over conventional telephone lines and through wireless communication.

The ATH command takes the phone off the hook.

Baud is limited to 2400 cycles per second. Baud rate is limited by the capability of copper wires to transmit signals. Bps represents the actual number of data bits that can be transmitted per second.

This chip is called a UART (universal asynchronous receiver-transmitter).

Three protocols for synchronous communication are Xmodem, Ymodem, and Zmodem.

Zmodem shares all the features found in Xmodem and Ymodem protocols. It also adds a few new features, including crash recovery, automatic downloading, and a streaming file-transfer method. It is the protocol of choice for most telecommunication operations.

Handshaking is the negotiation of the rules (protocols) of communication between two modems.

AT commands are text commands that can be used to provide instructions to a modem. They are all preceded by the letters "AT." These commands are very useful as diagnostic tools for today's computer professional. To use these commands, make sure the communication software is loaded and the computer is in terminal mode. Unless the modem is set up to autoconnect (online mode), it will be in command mode and ready to accept AT commands.

In half-duplex, the RJ-11 plug has only two wires; therefore, only one signal can be sent or received at a time. Half-duplex is used to send messages in only one direction, like a fire alarm signal.

In full-duplex, the RJ-12 plug uses four wires (for two phones). It is the same size as the RJ-11 but with two additional wires. This enables users to send and receive data simultaneously.

Asynchronous communication is data transmission in which the length of time between characters may vary. Timing is dependent on the actual time it takes for the transfer to occur. This differs from synchronous communication, which is timed rigidly by an external clock.

Synchronous communication is a form of communication in which blocks of data are sent at strictly timed intervals. Because of this timing, no start or stop bits are required. Synchronous communication is more reliable than asynchronous and, therefore, more widely used.

Faxes involve a different technology from that used by modems and are developed by different standards committees and operate on technology defined in a different standard than modems. A fax can be a stand-alone machine or incorporated into a computer. Computer faxes allow you to use the same format as picture reproduction (they paint a page of black-and-white pixels).

Null-modem cables are used to directly connect two computers together without the need for a modem. The transmit and receive wires in the cable (wires 2 and 3) are switched to make the computers "think" they are using modems.

You should always consider the total operating cost, including the cost of paper and ink or toner.

Bps stands for bits per second.

Here is a table of connectors. How many did you get right?

A 25-pin female connector is used for a parallel port on the computer.

The most common parallel connector on the printer is the Centronics connector.