+-+-+-+¢ PRINTER BASICS ¢ Everything You Wanted To Know About¢ Using Your Printer!¢ By John Picken and reprinted by Puget¢ Sound Atari News, Re-printed by THE¢ OL' HACKERS with THANKS¢ ********¢ Many computer owners claim the¢ "reaison d'etre" for their system is¢ productivity software - data base,¢ word processor, etc. At least, that's¢ how they justify the time and money¢ spent to a disbelieving spouse; after¢ all, Rule 1 of personal computing is:¢ "Never admit to owning a joystick".¢ Assuming the owner is actually going¢ to use the system for more than¢ PacMan, the most important component¢ becomes the printer. Application¢ software is nearly worthless without¢ a means of presenting permanent¢ results. Unfortunately, the printer¢ is often the most under utilized¢ component in a system because it is¢ the least understood. Using a printer¢ is not terribly complex though it¢ sometimes seems so because of the¢ instruction manual. Usually, all the¢ information you need to learn to¢ control any printer can be found in¢ its manual, albeit with some errors.¢ You often get better results by¢ regarding the manual as a collection¢ of hints to provide a basis for¢ experimentation. Why this is so is¢ anyone's guess, but you can add this¢ to the collected wisdom of Murphy:¢ "Quality of documentation varies¢ inversely with printer¢ sophistication." Printers come in all¢ shapes, sizes, and prices. They may¢ be broadly categorized by the way¢ they mark the paper. Laser machines¢ produce superb results at a superb¢ price. It is my understanding that¢ they print using techniques similar¢ to Xerography but I haven't really¢ looked into them because of lack of¢ opportunity (read "lack of dollars")¢ to play with one. "Letter Quality"¢ printers produce characters by the¢ single impact of a complete form,¢ whether it be on a wheel, drum, ball¢ or typewriter key. This category runs¢ from top of the line "Daisy Wheel"¢ machines down to the old Atari 1027.¢ Prices range from high to low and,¢ correspondingly, speeds from fast to¢ dead slow. All however, have two¢ common characteristics: First, if¢ character size and style is¢ changeable, it can only be¢ accomplished by replacing the¢ printing element. Second, they are¢ mechanically complex and usually¢ noisy.¢¢ "Dot Matrix", the most commonly¢ used printers, produce images by¢ patterns of dots similar to the way¢ an image is drawn on a television.¢ Dots may be formed by ink jets or¢ thermal paper but most commonly, are¢ produced by "pins" striking a ribbon¢ over the paper. "Nine-Pin" dot matrix¢ machines are the subject of¢ discussion. ¢¢ While it is possible to find older¢ models with fewer, the standard is¢ nine pins, though only eight are¢ normally used at any one time. The¢ pins, also called "wires", are¢ arranged in a vertical column. Images¢ are produced by moving this column¢ across the page while "firing" or¢ "striking" the pins in various¢ combinations. The difference from a¢ television is that the printer does¢ up to nine rows of pins at a time. ¢ Why use only eight of nine, and why¢ these numbers in the first place?¢ Well, eight is the closest thing you¢ will find to a "magic number" in the¢ world of computing because a "byte",¢ which is normally the smallest usable¢ amount of data, is always made up of¢ eight bits. The printer is able to¢ interpret the bits separately, so the¢ bits of a single byte can be used to¢ control firing of eight pins. ¢¢ The ninth pin is there for things¢ like underlining or descenders on¢ lower case letters. The printer¢ normally only uses eight pins but it¢ may switch between the top or bottom¢ eight. Try underlining on most¢ printers and you'll notice that the¢ underline runs into lower case¢ descenders. There are nine-pin¢ graphics modes but they are rarely¢ used as a complete second data byte¢ is required for the addition of only¢ one more pin. Essentially, you can¢ ignore the existence of the ninth pin¢ unless you want to get into the more¢ advanced subjects like download¢ characters. "27-pin", also called¢ "24-Pin", printers are nearly¢ identical, but have three such pin¢ columns mounted closely side by side¢ with a slight vertical offset between¢ each. This arrangement produces much¢ higher quality characters than is¢ possible with nine pins. Once you get¢ beyond simple text printing, these¢ become more complex as you obviously¢ need at least one byte to control¢ eight of the pins in each of the¢ three columns and the equivalent of¢ the nine-pin mode would require a¢ total of six data bytes. ¢¢ The key to understanding how dot¢ matrix printers work, and therefore,¢ what is and is not possible, lies in¢ the name. They cannot produce any¢ image other than a "Dot" - everything¢ they print is formed from dots. The¢ "Matrix" part of the name describes¢ something which, physically, does not¢ exist. It is a human concept¢ represented by a collection of bytes¢ for the printer's memory. The¢ printer's "Firmware" (program in ROM)¢ interprets these as a pattern of pins¢ to fire to form a particular¢ character. ¢¢ Mechanically, that's it: the printer¢ can produce only dots. Firmware and¢ software control pin firing, paper¢ feed, and carriage motion to arrange¢ these on the paper. ¢¢ While printer response to any¢ particular byte is governed by¢ firmware, this response can be¢ modified. Sometimes this can be done¢ by switches but many features are not¢ controllable except by software. In¢ other words, the computer must¢ command the printer remotely. ¢¢ Like any other kind of remote¢ control, communication is required. A¢ small part of this consists of actual¢ electronic signals. Most however is¢ exercised by the computer talking to¢ the printer in a language it¢ understands: patterns or sequences of¢ data bytes. This is where the user¢ enters the picture via a word¢ processor or other program. ¢¢ Getting what you want out of your¢ system requires you to give both the¢ printer and the word processor the¢ proper commands. The word processor¢ contains a block of data holding the¢ information it needs to control your¢ particular printer. This is¢ changeable, normally by load from¢ disk. There are numerous names used¢ to describe these: "Printer Driver",¢ "Printer Description", and¢ "Configuration" files being some of¢ the more common. No matter what¢ they're called, they are functionally¢ bilingual dictionaries which the word¢ processor uses to translate something¢ like "underline from here to here"¢ into language the printer¢ understands. ¢¢ If your system is not producing up¢ to its capabilities, the source of¢ the problem may very well be this¢ file. Most word processors come with¢ a utility program to allow you to¢ change or customize the printer¢ driver. The catch is you've got to¢ read and understand the¢ documentation, both for the word¢ processor and the printer, and you¢ have to know what is and is not¢ possible. Understanding of a few¢ terms and measurements aids in this¢ task. ¢¢ BUFFER -- "Buffer" is commonly used¢ but not always understood. A buffer¢ is just a reserved area of memory for¢ temporary storage of bytes. When¢ dealing with printers, there are at¢ least two buffers involved, one in¢ the computer and one in the printer.¢ Eight-bitters have a buffer in the¢ interface as well which serves the¢ same purposes as printer buffers.¢ Buffers allow transmission of¢ multiple byte blocks of data. This¢ decreases time lost on "Handshaking"¢ signals and calculation of checksums.¢ Also, since the printer can't print¢ anywhere near as fast as the computer¢ can send, it accepts and stores as¢ many bytes as it can so that the¢ computer is free to move on to other¢ business sooner. Obviously the bigger¢ the printer buffer, the sooner the¢ transmission is completed. ¢¢ The second purpose of the printer¢ (and interface) buffer is to allow it¢ to examine and modify the data before¢ it is printed. It has to sort out¢ printable data from commands, make¢ any required conversions such as¢ ATASCII, ASCII or addition of auto¢ line feeds, and possibly, calculate¢ right justification, etc. Once this¢ is done, it determines how, and at¢ what point in the printout, to apply¢ the commands. ¢¢ Most printers actually have two¢ buffers - everything that comes in¢ goes to the "Receive Buffer".¢ Printable stuff is then moved and¢ held in the "Print Buffer". ¢¢ The importance of this distinction¢ is that some commands affect only the¢ print buffer - you have to read and¢ decipher the book.¢ <><> END <><>¢
