Month: February 2009
Month: February 2009
The PCI-SIG, an industry organization dedicated to developing and enhancing PCI/PCI Express (PCIe) technology, has successfully developed the PCI, PCI-X and PCIe Gen 1 and Gen 2 interconnect protocols and promoted the deployment of these technologies since PCI's inception in 1992.
In early 2008, the PCI-SIG announced the establishment of a workgroup chartered with the development of the next generation of PCIe " the PCI Express Base Specification 3.0, or PCIe Gen 3.
The Gen 3 specification is yet another step forward in enhancing the usefulness of the PCIe protocol by doubling the effective bandwidth and adding protocol enhancements to increase end-system performance.
Leading up to this development, IBM and Intel in 2006 launched an initiative called Geneseo, proposing extensions to the PCIe protocol for high-performance computing and visual processing.
Recommendations from this initiative were provided to the PCI-SIG as potential PCIe protocol enhancements. In addition to the adoption of Geneseo, several other engineering change notices (ECNs) were released by the PCI-SIG, providing enhancements for the efficiency and usefulness of the PCIe protocol.
FPGA-Field Programmable Gate Array and CPLD-Complex Programmable Logic Device– both are programmable logic devices made by the same companies with different characteristics.
- "A Complex Programmable Logic Device (CPLD) is a Programmable Logic Device with complexity between that of PALs (Programmable Array Logic) and FPGAs, and architectural features of both. The building block of a CPLD is the macro cell, which contains logic implementing disjunctive normal form expressions and more specialized logic operations".
- Go to Wikipedia to get more information about it.
- Granularity is the biggest difference between CPLD and FPGA.
- FPGA are "fine-grain" devices. That means that they contain hundreds of (up to 100000) of tiny blocks (called as LUT or CLBs etc) of logic with flip-flops, combinational logic and memories.FPGAs offer much higher complexity, up to 150,000 flip-flops and large number of gates available.
How Programmable Logic Works
In recent years, the line between hardware and software has blurred. Hardware now engineers create the bulk of their new digital circuitry in programming languages such as VHDL and Verilog. This article will help you make sense of programmable logic.
A quiet revolution is taking place. Over the past few years, the density of the average programmable logic device has begun to skyrocket. The maximum number of gates in an FPGA is currently around 500,000 and doubling every 18 months. Meanwhile, the price of these chips is dropping. What all of this means is that the price of an individual NAND or NOR is rapidly approaching zero! And the designers of embedded systems are taking note. Some system designers are buying processor cores and incorporating them into system-on-a-chip designs; others are eliminating the processor and software altogether, choosing an alternative hardware-only design.
As this trend continues, it becomes more difficult to separate hardware from software. After all, both hardware and software designers are now describing logic in high-level terms, albeit in different languages, and downloading the compiled result to a piece of silicon. Surely no one would claim that language choice alone marks a real distinction between the two fields. Turing's notion of machine-level equivalence and the existence of language-to-language translators have long ago taught us all that that kind of reasoning is foolish. There are even now products that allow designers to create their hardware designs in traditional programming languages like C. So language differences alone are not enough of a distinction.
Introduction In the days of modern means of obtaining information ,Anyone with amost no knowledge can write code. Even teenagers can sling gates and PAL equations around. What is it that separates us from these amateurs? Do years of college necessarily make us professionals, or is there some other factor that clearly delineates engineers from hackers? With
A microcontroller is a computer with most of the necessary support chips
onboard. All computers have several things in common, namely:
- A central processing unit (CPU) that ‘executes’ programs.
- Some random-access memory (RAM) where it can store data that is variable.
- Some read only memory (ROM) where programs to be executed can be stored.
- Input and output (I/O) devices that enable communication to be established
with the outside world i.e. connection to devices such as keyboard, mouse,
monitors and other peripherals.
There are a number of other common characteristics that define microcontrollers.
If a computer matches a majority of these characteristics, then it can be
classified as a ‘microcontroller’. Microcontrollers may be:
Atoms and electrons
Everybody knows about atoms and electrons don't they? Well we could skip this part but of course we won't because you will likely learn something new.
Electron theory states all matter is comprised of molecules, which in turn are comprised of atoms, which are again comprised of protons, neutrons and electrons. A molecule is the smallest part of matter which can exist by itself and contains one or more atoms.
If you turn on a light switch for example you will see the light bulb (globe) glow and emit light into the room. So what caused this to happen? How does energy travel through copper wires to light the bulb? How does energy travel through space? What makes a motor turn, a radio play?
To understand these processes requires an understanding of the basic principles. For the light to glow requires energy to find a path through the light switch, through the copper wire and this movement is called electron flow. It is also called current flow in electronics. This is the first important principle to understand.
Development of Electromotive Force
• Faraday's Law
• Application of Faraday's Law
• A Single Coil DC Motor
• Motor Constants
In the early 1830’s, Michael Faraday and Joseph Henry independently discovered the relationship between changing magnetic fields and induced EMF in circuits. If B is the flux density of a constant magnetic field and a conductor is moved through this field at a velocity V, an EMF E is generated in the conductor such that:
If the conductor is part of a complete electrical circuit with a resistance R, then the EMF will produce a current in the conductor such that:
I = E / R = B x V / R
The development of an EMF in a conductor moving in a magnetic field is the principle on which many types of tachometers are based. By using the commutation
techniques described in the next section, a rotary device can be constructed which has, as its input, a rotary mechanical motion and, as its output, a voltage proportional to that input rotational velocity. Another specific application of Faraday’s Law is used in electric motors. That is, if a conductor of length L carrying a current I is placed in a magnetic field B, a magnetic force F is created such that:
• Calculating Mechanical Power Requirements
• Torque – Speed Curves
• Numerical Calculation
• Sample Calculation
• Thermal Calculations
Calculating Mechanical Power Requirements
Physically, power is defined as the rate of doing work. For linear motion, power is the product of force multiplied by the distance per unit time.
In the case of rotational motion, the analogous calculation for power is the product of torque multiplied by the rotational distance per unit time.
How To Select A DC Motor
Selecting a DC motor for a particular application can be a rather involved process . Hower, it is often useful to be able to "ballpark" a motor selection on one's own. A few rules relating to the physics and the practical application of motors should be kept in mind.
The major constraint on motor operation is thermal in nature. The heat a motor must dissipate can always be calculated as follows:
Heat dissipated = current through the motor squared, multiplied by the terminal resistance.
The current through a motor is solely determined by the torque the motor produces. Current and torque are related by the torque constant of the motor.
Current through motor = torque produced divided by the torque constant
DC Motor Application Considerations
Audible noise is a concern in some types of motor applications. In many medical applications like infusion pumps or prosthetic devices, the patient can be very sensitive to the noise disturbance. Good design practice requires that the noise be limited as much as possible. In large machines, the combination of hundreds of DC motors and gears operating simultaneously can be very loud and distracting to the employees who have to work in close proximity to the machine.
Quality Components: Probably the best method of insuring low audible noise in motors is to specify quality components. Motors using cheap or poorly fitted bearings are more likely to be noisy. Poorly designed or loose fitting brush sets can contribute to audibly noisy commutation. Manufacturers of inexpensive, high volume motors cannot reasonably be expected to concern themselves with quiet operation beyond some minimum standard, and the use of such motors in applications where quiet operation is important should be considered carefully. The designer must consider whether low cost takes precedence over quiet operation in the priorities of the customer.
Bearing Choice: The use of ball bearings without pre-load is a potential source of audible noise. Where the specific application permits, ball bearings should be pre-loaded. This means that the balls will not be able to move axially in the race and cause the minute intermittent rattling that can sometime be associated with unpreloaded ball bearings. Smaller ball bearings can be sensitive to heavy shaft loads. They are easily damaged during press fitting added components and by short radial or axial overloads. Care should be taken not to exceed the shaft loading ranges specified in the datasheets. A damaged ball bearing can be a significant source of audible noise and can effect motor life.