Proteus VSM

Published:2011/8/3 1:31:00 Author:Phyllis From:SeekIC

Also simulates microcontrollers!

By David Daamen

Schematic drawing, PCB designing and off you go testing the design. These days we do everything on a PC. Simulation programs have now reached a level of sophistication that includes co-simulation of a microcontroller in your design. Proteus VSM from Labcenter Electronics is an extensive software bundle offering professional features at an affordable price.

Proteus Virtual System modeling (VSM) is software that allows digital and analogue circuits, or a mixture of the two, to be simulated on a PC. Of course, it all starts with circuit diagram entry (’schematic capture’). Here, ISIS schematic capture is used. From the same supplier comes a separate utility, ARES, for the PCB design phase, providing a seamless link with ISIS. Together, ISIS and ARES form the traditional combination that makes ’putting a circuit onto PCB’ very easy indeed. Naturally we found features like connectivity verification (’electrical rule and connectivity check"), an automatic component placer and an automatic track router. So far, nothing unusual as other software products may be found with roughly the same functionality.

In the case of Proteus VSM, it’s the simulation part that offers a number of unusual features, including one we’ve not seen before in affordable design/simulation packages: microcontrollers may be included in the circuit. That, in itself, is possible with other design software, but Proteus VSM is actually capable of simulating the code executed by the micro! Again, you may argue that even that is not unique but wait, there’s another novelty. During simulation, you can work interactively with the circuit: switches and potentiometers may be operated ’as if for real’ and the status of LEDs or information on LCDs is immediately visible. The feature is fast, too, as it is perfectly possible to make periodic signals with frequencies in the audio range audible via the PC’s soundcard. A complete graphic LCD touch screen hooked up to a microcontroller is not only refreshed during simulation, but may also be controlled using the mouse. It all happens virtually in real-time. On a 300-MHz Pentium n you can simulate a standard 8051 system ticking at 12 MHz.

The simulator

The core of the simulator is called ProSPICE, a combination of an analogue simulator and a fast event-driven digital simulator, allowing a mix of analogue and digital electronics (a ’mixed mode’ circuit) to be simulated without problems. The advantage of SPICE is that component models supplied by manufacturers may be added at the drop of a hat. Incidentally, Proteus VSM comes with about 6,000 SPICE models.

The simulation also employs ’animated models’: graphic animations whose appearance can change during simulation, for example, to indicate the current flow direction, or showing that a lamp actually lights up. It is also possible to define your own (animated) models, in principle, without the need to program them!

A documented ’software developers kit’ (SDK) is supplied allowing models to be created in the form of DLL files.

Measuring

Virtual testing implies virtual measurement — not just using simple volt and ammeters, but also more advanced instruments like an oscilloscope, a function generator, a pattern generator, a counter and an asynchronous terminal. As far as operation and options are concerned, these are simply ’instruments’ as you may see them on the test bench. A useful ’extra’ is the ability to display the logic level of any connection or junction in the circuit in real time using a colored dot. More advanced measurements like graph plotting or frequency response measurement, noise and distortion analysis, are available in the utility ’Advanced Simulation Option’.

Microcontroller co-simulation

VSM is capable of linking two simulations: one of software executed ’inside’ a microprocessor, the other, of the complete electronics circuit around the micro. For example, the act of a processor writing code to a port results in corresponding logic level changes in the circuit. And the other way around: if a (sub-)circuit changes a logic level then the simulated program will notice it.

VSM’s included models not just support simple I/O ports but also interrupts, timers, USARTs etc. — depending of course on the processor being simulated. It is even possible to include multiple processors in the circuit — it’s just a matter of drawing a few lines to connect the relevant chips! At the time of writing, Proteus VSM versions are available for the BASIC Stamp, PIC, AVR, HC11 and 8051 processors.

Debugging

Because the design of a microprocessor or microcontroller circuit is hardly ever finished and approved in one go, the process of debugging or ’error elimination’ remains essential. Not surprisingly, Proteus VSM gives great attention to the subject. In particular the single-stepping feature will be welcomed by designers. Just as with the software debugger you normally use, code for the processor may be executed line by line. However, this time you can observe the results of the code execution on the whole circuit rather than the micro alone. Depending on the processor family selected and available programming tools it is even possible to ’step’ through code written in higher programming languages like C.

Proteus VSM is highly recommended for designers frequently working on circuits containing digital as well as analogue electronics.

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