+-+-+-+›         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 <><>›