How many versions of VHDL are there?

There are four. The original release of the VHDL language occurred in 1987 with the adoption of the Language Reference Manual as an IEEE standard. In 1993, the IEEE-1076 standard was modified and ratified and became known as VHDL'93. This is now widely supported. In 2000, the VHDL 1076 2000 Edition appeared - this fixed shared variables by introducing the idea of protected types. Finally, VHDL 1076-2002 appeared. This includes protected mode types, but also changes ports of mode buffer to make them more usable, along with some other small changes. In practice, VHDL 1076-1993 is the current flavor of VHDL which is widely supported by tool vendors.

How must I write VHDL to make it synthesizable?

Because large parts of the language make no sense in a hardware context, synthesizable VHDL is a relatively small subset of VHDL. You must stick to this subset, and understand exactly how the synthesis tool you use interprets that code. For FPGA in particular you must also develop a good understanding of the structure of your chip, and know how your code must reflect the most efficient use of that structure. Fundamentally, never forget that you are designing a circuit, not writing a program. Forgetting this simply but important fact will only lead to pain later.

Can I use VHDL for the analog part of a design?

Yes and No. Yes, there is a VHDL Analogue and Mixed Signal language (VHDL-AMS), based on VHDL 93, which allows modeling of both analogue and digital in the same language. However the idea of analogue synthesis is still in its early days, so currently you wouldn't normally be able to go on and synthesize an analogue model written in VHDL-AMS. There's a VHDL-AMS website at www.eda.org/vhdl-ams.

What is the difference between VHDL and Verilog?

Fundamentally speaking, not a lot. You can produce robust designs and comprehensive test environments with both languages, for both ASIC and FPGA. However, the two languages approach the task from different directions; VHDL, intended as a specification language, is very exact in its nature and hence very verbose. Verilog, intended as a simulation language, it much closer to C in style, in that it is terse and elegant to write but requires much more care to avoid nasty bugs. VHDL doesn't let you get away with much; Verilog assumes that whatever you wrote was exactly what you intended to write. If you get a VHDL architecture to compile, it's probably going to approximate to the function you wanted. For Verilog, successful compilation merely indicates that the syntax rules were met, nothing more. VHDL has some features that make it good for system-level modeling, whereas Verilog is much better than VHDL at gate-level simulation.

Intel marks 40 years of the 4004 microprocessor

A 1971 breakthrough that changed the world

CHIPMAKER Intel today celebrates the 40th anniversary of the 4004, the world's first commercially available microprocessor.

To call Intel's 4004 just a microprocessor is to do the microelectronics world a great disservice. Not only was the Intel 4004 the first commercial microprocessor, shattering what people thought of computers, it signaled Intel's shift away from manufacturing memory and into what was going to become the industry that changed the world forever.

Back in 1969 when Japanese calculator outfit Nippon Calculating Machine Corporation asked Intel to design 12 chips for a business calculator called Busicom, Intel had already achieved some success with its memory business. Although Intel was far from being a market leader, the two 'Fairchildren', Robert Noyce and Gordon Moore were busy making money fabbing RAM chips, but not for much longer.

Back in 1969, Intel didn't have the luxury of saying no to business and Federico Faggin, Ted Hoff and Masatoshi Shima got to work on designing a processor for the relatively mundane business calculator. Later Hoff remarked that in the late 1960s it simply wasn't feasible to talk about personal computers.

Like the birth of many revolutionary pieces of engineering, the 4004 was designed by a bunch of engineers working into the night on the promise of creating something completely different.

While Faggin, who had also worked at Fairchild Semiconductor with Noyce and Moore, was busy designing the 4004 Hoff is widely credited with coming up with the architecture. Faggin built Hoff's architecture, with the legend saying that the first wafers came back to Intel's Santa Clara offices at 6PM just as everyone was clocking out for the day. Faggin pulled an all nighter in the lab to check whether the first baked 4004 actually worked, and at 3AM, overcome with exhaustion and satisfied that the radical 4004 did the job, he went home to tell his wife, "It works!".

Faggin was so proud of his design that he etched his initials, FF, on one side of the 4004's design. In later iterations of the 4004 the initials were moved, but just like an artist, Faggin signed his own work. And make no mistake, the 4004 processor is a work of art.

It might sound bashful, but Intel's 4004 wasn't particularly powerful, and the firm admitted, "The 4004 was not very powerful, it was primarily used to perform simple mathematical operations in a calculator called Busicom." However Noyce and Moore realised that it wasn't the 4004 itself that was important but its architecture.

In terms of complexity, Intel's 4004 had 2,300 MOS transistors and was fabricated on a 10,000nm process node on 60mm wafers. In a graphic illustration of Moore's law, processors from Intel and AMD today typically have hundreds of millions of transistors and are fabricated on the 32nm process node on 300mm wafers. But the numbers simply don't tell the whole story, the fact is that the 4004 was not just a new chip with a new micro-architecture, but it was a radical new way of thinking and building processors.

What Faggin, Hoff and Shima had created with the 4004 was the ability to commoditise computing by adding the micro in microprocessors. Prior to the 4004, general purpose computers were the hulking machines you saw in black-and-white films as room-sized equipment. Henry Ford brought the motorcar to the wider public through mass production, while Intel brought computing to the masses by miniaturising it.

Intel showed what would become perhaps the first known example of its shrewd business policies by offering Busicom, now a company in its own right, a reported $60,000 for the design and marketing rights for the 4004. Busicom agreed to the deal and, even though a year later the firm went bust, Intel was left with the ability to sell the 4004, which it did in 1971.

In what would become standard Intel behaviour, the firm courted developers for its 4004 processor. Even at that time, Intel knew that software held the key to its success, and it wasn't wrong.

Like Noyce and Moore, Faggin chose to form his own company in 1974 called Zilog. The firm is extremely successful in embedded CISC processors but is best known for producing chips that were found in the Sinclair ZX Spectrum. Faggin still heads up Zilog but his name will forever be associated with the creation of arguably the 20th century's most important innovation in electronics. Shima followed Faggin to Zilog in 1975 and worked on the Z80 and Z8000.

Hoff stayed on at Intel, becoming an Intel Fellow and more recently was awarded the National Medal of Technology and Innovation in 2009 by US President Barack Obama, a year before Faggin received the same award.

What Faggin, Hoff and Shima created wasn't just a microprocessor, it was a blueprint for others to follow and quite simply extended what was thought possible. Credit should be given to Noyce, Moore and Intel's third co-founder, Andy Grove, for letting the electronics engineers have the time and resources to develop what was perhaps the most important, ground-breaking electronic component created in the past century. µ

Best Ebooks for Digital Designing

1. Digital Design and Computer Architecture
2. Complete Digital Design: A Comprehensive Guide to Digital Electronics and Computer System Architecture
3. Schaum's Outline of Digital Principles
4. Digital Design: Principles and Practices Package (4th Edition)
5. Digital Design for Print and Web: An Introduction to Theory, Principles, and Techniques

Silicon Blue launches 40nm fgpas

Programmable logic developer Silicon Blue is sampling the iCE40 mobileFPGA family, which includes devices targeted at smartphones and tablets. Fabricated on TSMC's 40nm low power standard cmos process, the LP and HX families provide twice the logic capacity of the company's 65nm iCE65 devices. "We've proven our technology leadership with iCE65 and are on track to ship approximately 10million units this year," said ceo Kapil Shankar. The LP series, aimed at smartphones, and the HX series, designed with tablets in mind, offer sensor management and high speed custom connectivity. Silicon Blue calls its technology Custom Mobile Devices (CMDs). There are five devices in both series, with capacities ranging from 640 to 16,192 logic cells. However, while the HX range offers higher performance, it consumes more power. Both versions come in 2.5 x 2.5mm micro plastic bgas, Shankar added: "We've taken the next bold step with CMDs by extending video performance capability for smartphones to 525Mbit/s, enabling HD720p 60Hz (1280 x 720) and HD1080p 30Hz (1920 x 1080). For tablets, CMDs can now support WUXGA (1920x1200) with dual LVDS, HD720p 60Hz (1280x720) and HD1080p 30Hz (1920x1080)."

Another 40nm family, code named San Francisco, will be announced later in 2011.