Laser Printers

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Laser Printers

• Using MIPS

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Path of paper through laser printer

• The primary principle at work in a laser
  printer is static electricity. Static electricity
  is simply an electrical charge built up on an
  insulated object. Since oppositely charged atoms
  are attracted to each other, objects with
  opposite static electricity fields cling
  together. A laser printer uses this phenomenon as
  a sort of "temporary glue." The core component of
  this system is the photoreceptor, typically a
  revolving drum or cylinder. This drum assembly is
  made out of highly photoconductive material that
  is discharged by light photons.

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• Initially, the drum is given a total positive
  charge by the charge corona wire, a wire with an
  electrical current running through it. As the
  drum revolves, the printer shines a tiny laser
  beam across the surface to discharge certain
  points. In this way, the laser "draws" the
  letters and images to be printed as a pattern of
  electrical charges -- an electrostatic image.
  After the pattern is set, the printer coats the
  drum with positively charged toner -- a fine,
  black powder. Since it has a positive charge, the
  toner clings to the negative discharged areas of
  the drum, but not to the positively charged
  "background."

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With the powder pattern affixed, the drum
rolls over a sheet of paper, which is moving
along a belt below. Before the paper rolls under
the drum, it is given a negative charge by the
transfer corona wire (charged roller). This
charge is stronger than the negative charge of
the electrostatic image, so the paper can pull
the toner powder away. Since it is moving at the
same speed as the drum, the paper picks up the
image pattern exactly. To keep the paper
from clinging to the drum, it is discharged by
the detac corona wire immediately after picking
up the toner.
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• Finally, the printer passes the paper through
  the fuser, a pair of heated rollers. As the paper
  passes through these rollers, the loose toner
  powder melts, fusing with the fibers in the
  paper. The fuser rolls the paper to the output
  tray, and you have your finished page. The fuser
  also heats up the paper itself, of course, which
  is why pages are always hot when they come out of
  a laser printer.
• After depositing toner on the paper, the drum
  surface passes the discharge lamp. This bright
  light exposes the entire photoreceptor surface,
  erasing the electrical image. The drum surface
  then passes the charge corona wire, which
  reapplies the positive charge.

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The Controller

• Before a laser printer can do anything else,
  it needs to receive the page data and figure out
  how it's going to put everything on the paper.
  This is the job of the printer controller. The
  printer controller is the laser printer's main
  onboard computer. It talks to the host computer
  (for example, your PC) through a communications
  port, such as a parallel port. At the start of
  the printing job, the laser printer establishes
  with the host computer how they will exchange
  data. The controller may have to start and stop
  the host computer periodically to process the
  information it has received.
• Printer
  Controller Inputs

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Parallel Port

• The original specification for parallel
  ports was unidirectional, meaning that data only
  traveled in one direction for each pin. With the
  introduction of the PS/2 in 1987, IBM offered a
  new bidirectional parallel port design. This mode
  is commonly known as Standard Parallel Port (SPP)
  and has completely replaced the original design.
  Bidirectional communication allows each device to
  receive data as well as transmit it. Many devices
  use the eight pins (2 through 9) originally
  designated for data. Using the same eight pins
  limits communication to half-duplex, meaning that
  information can only travel in one direction at a
  time. But pins 18 through 25, originally just
  used as grounds, can be used as data pins also.
  This allows for full-duplex (both directions at
  the same time) communication.

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The Controller Language

• For the printer controller and the host computer
  to communicate, they need to speak the same page
  description language. The primary printer
  languages these days are Hewlett Packard's
  Printer Command Language (PCL) and Adobe's
  Postscript. Both of these languages describe the
  page in vector form -- that is, as mathematical
  values of geometric shapes, rather than as a
  series of dots (a bitmap image). The printer
  itself takes the vector images and converts them
  into a bitmap page. With this system, the printer
  can receive elaborate, complex pages, featuring
  any sort of font or image. Also, since the
  printer creates the bitmap image itself, it can
  use its maximum printer resolution.

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The Controller Language - continued

• Some printers use a graphical device interface
  (GDI) format instead of a standard PCL. In this
  system, the host computer creates the dot array
  itself, so the controller doesn't have to process
  anything -- it just sends the dot instructions on
  to the laser. But in most laser printers, the
  controller must organize all of the data it
  receives from the host computer. This includes
  all of the commands that tell the printer what to
  do -- what paper to use, how to format the page,
  how to handle the font, etc. For the controller
  to work with this data, it has to get it in the
  right order.
• In most laser printers, the controller saves all
  print-job data in its own memory. This lets the
  controller put different printing jobs into a
  queue so it can work through them one at a time.
  It also saves time when printing multiple copies
  of a document, since the host computer only has
  to send the data once.

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Printer Speed

• It may seem perfectly natural, when judging
  the performance of a high-speed laser printer, to
  look at the clock speed of the processor that's
  driving it. The more megahertz, the better,
  right?Not necessarily.
• Clock speed - an indication of how many
  instructions per second a processor can execute -
  as the measure of performance in PCs. And many
  consider it the driving force behind printer
  speed, which is the number of pages per minute a
  printer can generate.
• There's more to print speed than clock speed
• Is the processor RISC or CISC?
• How fast does it process large graphics files and
  the very long algorithms characteristic of PCL
  and Adobe PostScript printer languages?
• And, bottom line, how much does it cost?

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CISC vs. RISC architecture

• Computing architecture affects both the speed and
  cost of laser printers.
• CISC (complex instruction set computer) have a
  much lower effective speed in an embedded
  application like a laser printer. That's because
  the CISC architecture was designed for computers.
• CISC chips are burdened by multi-cycle,
  micro-coded, complex instructions - a legacy of
  1970s development -- many of which are not
  required in embedded applications. Aside from
  performance, it can negatively impact the cost of
  other system components, including the
  electronics, power supply and pin count - a
  detriment to cost-sensitive embedded applications
  like laser printers.
• RISC (reduced instruction set computer)
  architecture was developed in the 1980s as a
  simpler, faster, superior alternative to CISC. It
  offers easier decoding and pipelining, and
  typically executes at least one instruction per
  clock cycle, as opposed to CISC, which often does
  less.

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MIPS architecture

• Of the current RISC architectures, the MIPS
  architecture is the only one in the embedded
  systems industry generally available for
  licensing.
• They range from ultra-low-power 32-bit CPU cores
  occupying less than a half-millimeter of silicon,
  to 64-bit dual-core processors running at 1 GHz.
• Cores are designed for easy integration into
  system-on-a-chip designs, which offer additional
  performance advantages in embedded applications,
  such as lower power and fewer components for
  higher reliability and out-of-the-box
  functionality.

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Example HP LaserJet 9500

• PMC-Sierra is the manufacturer of MIPS-based
  processors used in Hewlett-Packard laser
  printers. PMC-Sierras latest processor, 64-Bit
  MIPS RISC Microprocessor with integrated L2
  Cache, is used in the latest network printers
  from HP. The processor features 600MHz operating
  frequency, 2 levels of cache
• 1st level 16KB 4-way set associative 32-byte
  line size Instruction and Data caches,
• 2nd level 256 KB 4-way set associative 32-byte
  line size,
• Also, an L3 external cache (off chip)
  512KB-8MB direct-mapped, 32-byte line size

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Example HP LaserJet 9500 64-Bit Processor
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Will Printers become faster ?

• Future generations of workgroup printers will
  continue to offer increasingly higher speeds.
• Given the uniquely broad range of processors
  being designed by MIPS licensees, from
  ultra-low-power 32-bit cores to 64-bit 1-GHz
  CPUs, anything is possible.

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Thank you

• Questions?

Ramiz Bleibel Anton Petrosyan Mohamad
Ghuneim Bertha Sierra