[Design Application]
Leverage Flash-Based Microcontrollers To Cut Time-To-Market
Flash MCUs Shrink Development Time, While Helping Designers Respond To Customer Needs.
With product life cycles now measured in months rather than years, time to market is more important than ever in the success of a design—especially in the consumer market. Shorter design cycles also translate into less money spent on development and a faster return on investment. But the demands consumers make—more features, smaller sizes, and lower cost—tend to extend design cycles. Reprogrammable flash-based microcontrollers can help designers meet the demands of both customers and corporate bean counters.
Several years ago, a product could be taken from concept to production in a few months. To satisfy their consumer-market customers, however, designers must now integrate more functions onto a single chip and use software to differentiate models. With the level of integration in embedded processors growing and software complexity increasing, design cycles are doubling or tripling.
To compound the problem, device packages are becoming smaller. In some cases, the device die itself is used in the product. These fine-lead-pitch packages and chip-on-board assembly techniques can create roadblocks to emulation and debugging.
But reprogrammable flash-based microcontrollers offer advantages that can reduce the time to market. Flash technology doesn't only shorten the design cycle. It also provides a low-cost emulation solution in situations where none existed previously. Flash-based devices can be reprogrammed more quickly than EPROM-based circuits because flash memories don't require a lengthy exposure to UV light. Plus, flash-based chips don't have to be removed from the circuit board for reprogramming. Just attach a programming cable from the software-development tool to the board (assuming the board is designed for such a capability). Such a scheme eliminates other delays that slow the development process, such as the time for manual removal/insertion, fixing bent pins, etc.
Designers have basically three methods they can use to develop a product: simulation, "burn and learn," and emulation. Simulators for embedded products are typically free or very inexpensive. Usually only the program flow and initialization code can be verified, however. Any interaction with external circuitry is extremely limited.
Simulation can be used in conjunction with the burn-and-learn (BL) approach to speed the debug stage of the application-development cycle. BL typically refers to the method by which the designer programs a device, inserts it into the application, and monitors the operation of the circuit with an oscilloscope or logic analyzer. The way the circuit operates gives the designer clues about the code changes that will be required to make the circuit functional.
EPROM-based processors can lengthen development time because it usually takes 30 minutes or more to first erase and then reprogram the chip with the updated code. One way to speed up that approach is to purchase multiple, EPROM-based microcontroller units (MCUs). That way, the designer doesn't have to wait for one to erase before programming another. But this can be costly and irksome. The MCUs must be housed in more expensive, quartz-windowed packages. And the designer must keep track of which program version is programmed into which chip.
Devices with flash-based, electrically erasable memory can take a big chunk out of development time and cost. Most high-volume applications use an in-circuit programming technique in which the device is soldered into the circuit. It is then programmed through a cable from the programmer. One of the greatest strengths of flash-based devices, though, is that the processor doesn't have to be removed from the application, programmed, and then replaced. This reduces or eliminates the possibility of bent leads and ESD damage due to handling. The designer can still use the BL method, but only needs one device that doesn't have a lengthy erase cycle and doesn't need to be removed from the circuit.
The third development method is emulation. In-circuit-emulator (ICE) tools are the ultimate debugging approach, because they give the designer an "inside look" at the operation of the processor and code. Problems usually can be found immediately using single stepping or breakpoints, and by having access to register contents (both to view and alter). But all this power does not come free.
ICE tools are typically very expensive and have some inherent problems. The probe, which connects the ICE to the application, usually has some type of ESD or other circuit-protection devices that can interfere with the circuit's operation, often slowing it up. Also, the probe is connected to the circuit via a cable or other interconnect that introduces capacitance and loading effects on both the application circuit and probe. This is most apparent in an analog circuit, where the processor has an analog-to-digital converter (ADC).
Still another issue is that the probes support a limited number of package types. Dual-in-line and plastic-leaded-chip-carrier packages (DIP and PLCC) are most prevalent because the probe can be connected to the corresponding socket in the application. Small-outline IC adapters that are soldered onto the application's printed-circuit board are also readily available, but are often quite costly.
The fine-lead-pitch packages like shrink-small-outline and quad-sided flat packages currently are not supported by most probes. And even smaller approaches like chip-on-board (COB) and chip-scale-packaging (CSP) schemes present still more difficult, if not impossible, challenges to probe attachment. Such schemes push the designer into a corner in which flash-based processors and BL techniques are the only viable solution.
When using fine-lead-pitch packages or COB approaches, an extra step may be used in the development process. Simple applications can usually go right to the surface-mount design, but more complex applications require emulation. Since no emulation solution is available for these package types, a designer would first perform most of the debugging and development with a leaded prototype. Then, for production, the designer would switch to the surface-mount design. In this scenario, emulation needs have been satisfied. But cost and time-to-market have grown because of the extra prototype step.
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