Electronic Design

Digital Signal Controllers Take On Power, Programming Jobs

Digital signal controllers (DSCs) are making a splash in more than one area. They're available from a number of vendors, including Analog Devices, Microchip, and Texas Instruments. They look like a mix between a digital signal processor (DSP) and a RISC processor, plus a host of microcontroller peripherals.

DSCs are a hit in motor control, soft modems, multimedia support, power-supply control, and other applications. This covers a lot of ground, but embedded developers have been signing up to use DSCs as general-purpose devices, too. Their architecture handles interrupts well, and most can push the system state on the stack so multitasking operating systems can be employed.

DSC architectures are relatively new compared to many legacy architectures. The latest architectures are designed to support C, the programming language of choice for embedded developers.

Texas Instruments' TMS320F280x series marks the new trend in application-specific DSCs (see the figure). It incorporates a large flash memory with a prefetch queue that delivers single-cycle execution for inline code. Average execution time is 0.9 instructions per cycle. This is comparable to a cache-based system, but the TMS320F280x design incurs minimal hardware overhead.

Also, a large on-chip RAM can be used for code or data. The chip executes instructions in a single cycle with no penalty for branching, enabling developers to copy time-critical code into RAM. This must be done judiciously, since the chips don't support off-chip memory.

The TMS320F280x's processor core is based on the C28x with a 32- by 32-bit multiplier. It also has read-modify-write support required for multitasking.

The key to the TMS320F280x's ability to control switching power supplies lies in its ePWM (enhance pulse-width modulation) support, which provides accuracy that's almost 100 times that of the competition with improved resolution. The chip then can be used in designs that would otherwise require analog support or a very high-performance DSP.

The enhanced capture module (eCAP) and enhanced quadrature encoder pulse (eQEP) module help in signal- and motor-control applications. These subsystems require minimal processor intervention.

A 16-channel, 12-bit, high-speed analog-to-digital converter (ADC) operates at 6.25 Msamples/s. It has two sample-and-hold interfaces as well as flexible internal and external voltage references.

The chip family supports a range of communication peripherals, including serial peripheral interface (SPI), serial ports, I2C, and control-area network (CAN).

Pricing for the TMS320F2801 starts at under $5. The full-blown TMS320-F2808 costs less than $10.

Texas Instruments

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