Laser PrintersLaser Printers

Using MIPSUsing MIPS

Path of paper through laser Path of paper through laser printerprinter

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

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

With the powder pattern affixed, With the powder pattern affixed, the drum rolls over a sheet of the drum rolls over a sheet of paper, which is moving along a paper, which is moving along a belt below. Before the paper rolls belt below. Before the paper rolls under the drum, it is given a under the drum, it is given a negative charge by the negative charge by the transfer transfer corona wirecorona wire (charged roller). (charged roller). This charge is stronger than the This charge is stronger than the negative charge of the negative charge of the electrostatic image, so the paper electrostatic image, so the paper can pull the toner powder away. can pull the toner powder away. Since it is moving at the same Since it is moving at the same speed as the drum, the paper speed as the drum, the paper picks up the image pattern picks up the image pattern exactly. exactly.

To keep the paper from clinging To keep the paper from clinging to the drum, it is discharged by to the drum, it is discharged by the detac corona wire the detac corona wire immediately after picking up the immediately after picking up the toner.toner.

Finally, the printer passes the Finally, the printer passes the paper through the paper through the fuserfuser, a , a pair of heated rollers. As the pair of heated rollers. As the paper passes through these paper passes through these rollers, the loose toner powder rollers, the loose toner powder melts, fusing with the fibers in melts, fusing with the fibers in the paper. The fuser rolls the the paper. The fuser rolls the paper to the output tray, and paper to the output tray, and you have your finished page. you have your finished page. The fuser also heats up the The fuser also heats up the paper itself, of course, which is paper itself, of course, which is why pages are always hot why pages are always hot when they come out of a laser when they come out of a laser printer. printer.

After depositing toner on the After depositing toner on the paper, the drum surface paper, the drum surface passes the passes the discharge lampdischarge lamp. . This bright light exposes the This bright light exposes the entire photoreceptor surface, entire photoreceptor surface, erasing the electrical image. erasing the electrical image. The drum surface then passes The drum surface then passes the charge corona wire, which the charge corona wire, which reapplies the positive charge. reapplies the positive charge.

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

Printer Controller Inputs Printer Controller Inputs

Parallel PortParallel Port The original specification for The original specification for

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

The Controller Language The Controller Language

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

The Controller Language - continuedThe Controller Language - continued

• Some printers use a Some printers use a graphical device interfacegraphical device interface (GDI) format instead of a standard PCL. In this (GDI) format instead of a standard PCL. In this system, the host computer creates the dot array system, the host computer creates the dot array itself, so the controller doesn't have to process itself, so the controller doesn't have to process anything -- it just sends the dot instructions on to anything -- it just sends the dot instructions on to the laser. But in most laser printers, the controller the laser. But in most laser printers, the controller must organize all of the data it receives from the must organize all of the data it receives from the host computer. This includes all of the commands host computer. This includes all of the commands that tell the printer what to do -- what paper to use, that tell the printer what to do -- what paper to use, how to format the page, how to handle the font, etc. how to format the page, how to handle the font, etc. For the controller to work with this data, it has to For the controller to work with this data, it has to get it in the right order.get it in the right order.

• In most laser printers, the controller saves all print-In most laser printers, the controller saves all print-job data in its own memory. This lets the controller job data in its own memory. This lets the controller put different printing jobs into a put different printing jobs into a queuequeue so it can so it can work through them one at a time. It also saves time work through them one at a time. It also saves time when printing multiple copies of a document, since when printing multiple copies of a document, since the host computer only has to send the data once. the host computer only has to send the data once.

Printer SpeedPrinter Speed

It may seem perfectly natural, when judging the It may seem perfectly natural, when judging the performance of a high-speed laser printer, to look at the performance of a high-speed laser printer, to look at the clock speed of the processor that's driving it. The more clock speed of the processor that's driving it. The more megahertz, the better, right?megahertz, the better, right?Not necessarily. Not necessarily.

Clock speed - an indication of how many instructions per Clock speed - an indication of how many instructions per second a processor can execute - as the measure of second a processor can execute - as the measure of performance in PCs. And many consider it the driving force performance in PCs. And many consider it the driving force behind printer speed, which is the number of pages per behind printer speed, which is the number of pages per minute a printer can generate.minute a printer can generate.

There's more to print speed than clock speed:There's more to print speed than clock speed:• Is the processor RISC or CISC? Is the processor RISC or CISC? • How fast does it process large graphics files and the very How fast does it process large graphics files and the very

long algorithms characteristic of PCL and Adobe PostScript long algorithms characteristic of PCL and Adobe PostScript printer languages? printer languages?

• And, bottom line, how much does it cost? And, bottom line, how much does it cost?

CISC vs. RISC architectureCISC vs. RISC architecture

• Computing architecture affects both the speed and cost of laser Computing architecture affects both the speed and cost of laser printers.printers.

• CISC (complex instruction set computer) have a much lower CISC (complex instruction set computer) have a much lower effective speed in an embedded application like a laser printer. effective speed in an embedded application like a laser printer. That's because the CISC architecture was designed for That's because the CISC architecture was designed for computers.computers.

• CISC chips are burdened by multi-cycle, micro-coded, complex CISC chips are burdened by multi-cycle, micro-coded, complex

instructions - a legacy of 1970s development -- many of which instructions - a legacy of 1970s development -- many of which are not required in embedded applications. Aside from are not required in embedded applications. Aside from performance, it can negatively impact the cost of other system performance, it can negatively impact the cost of other system components, including the electronics, power supply and pin components, including the electronics, power supply and pin count - a detriment to cost-sensitive embedded applications like count - a detriment to cost-sensitive embedded applications like laser printers.laser printers.

• RISC (reduced instruction set computer) architecture was RISC (reduced instruction set computer) architecture was

developed in the 1980s as a simpler, faster, superior alternative developed in the 1980s as a simpler, faster, superior alternative to CISC. It offers easier decoding and pipelining, and typically to CISC. It offers easier decoding and pipelining, and typically executes at least one instruction per clock cycle, as opposed to executes at least one instruction per clock cycle, as opposed to CISC, which often does less. CISC, which often does less.

MIPS MIPS architecturearchitecture• Of the current RISC architectures, the MIPS Of the current RISC architectures, the MIPS

architecture is the only one in the embedded architecture is the only one in the embedded systems industry generally available for licensing. systems industry generally available for licensing.

• They range from ultra-low-power 32-bit CPU cores They range from ultra-low-power 32-bit CPU cores occupying less than a half-millimeter of silicon, to occupying less than a half-millimeter of silicon, to 64-bit dual-core processors running at 1 GHz.64-bit dual-core processors running at 1 GHz.

• Cores are designed for easy integration into Cores are designed for easy integration into system-on-a-chip designs, which offer additional system-on-a-chip designs, which offer additional performance advantages in embedded performance advantages in embedded applications, such as lower power and fewer applications, such as lower power and fewer components for higher reliability and out-of-the-components for higher reliability and out-of-the-box functionality. box functionality.

Example: HP LaserJet 9500Example: HP LaserJet 9500

PMC-Sierra is the manufacturer of MIPS-PMC-Sierra is the manufacturer of MIPS-based processors used in Hewlett-Packard based processors used in Hewlett-Packard laser printers. PMC-Sierra’s latest laser printers. PMC-Sierra’s latest processor, 64-Bit MIPS RISC processor, 64-Bit MIPS RISC Microprocessor with integrated L2 Cache, Microprocessor with integrated L2 Cache, is used in the latest network printers from is used in the latest network printers from HP. The processor features 600MHz HP. The processor features 600MHz operating frequency, 2 levels of cache:operating frequency, 2 levels of cache:

11stst level 16KB 4-way set associative 32- level 16KB 4-way set associative 32-byte line size Instruction and Data caches,byte line size Instruction and Data caches,

22ndnd level 256 KB 4-way set associative 32- level 256 KB 4-way set associative 32-byte line size,byte line size,

Also, an L3 external cache (off chip) Also, an L3 external cache (off chip) 512KB-8MB direct-mapped, 32-byte line 512KB-8MB direct-mapped, 32-byte line size size

Example: HP LaserJet 9500 64-Bit ProcessorExample: HP LaserJet 9500 64-Bit Processor

Will Printers become Will Printers become faster ?faster ?• Future generations of workgroup printers Future generations of workgroup printers

will continue to offer increasingly higher will continue to offer increasingly higher speeds.speeds.

• Given the uniquely broad range of Given the uniquely broad range of processors being designed by MIPS processors being designed by MIPS licensees, from ultra-low-power 32-bit cores licensees, from ultra-low-power 32-bit cores

to 64-bit 1-GHz CPUs, anything is possible.to 64-bit 1-GHz CPUs, anything is possible.

Thank youThank you Questions?Questions?

Ramiz BleibelRamiz Bleibel

Anton PetrosyanAnton Petrosyan

Mohamad GhuneimMohamad Ghuneim

Bertha SierraBertha Sierra