Prices for 32-bit microcontrollers continue to drop as Luminary Micro releases a new crop of 32-bit ARM Cortex-M3-based chips under $6. The 25/50-MHz Stellaris chips incorporate a 100-mA, 2.5-V low-dropout voltage regulator, brownout detection/power-on reset, and a temperature sensor. While these features are common in 8-bit micros, typically they're external components in many 32-bit solutions.
Assembler need not apply, as the system is designed for complete C/C++ programming. This includes all of the aspects of interrupt service routines, making solutions easier to create and maintain. Tools from ARM/Keil, IAR, GNU gcc, and others already are available. The native instruction set is the compact Thumb2.
A development kit priced at only $249 includes freeRTOS, Pumpkin Salvo, uC/OS-II, and Express Logic Threadx samples. Log on to Luminary Micro's Web site to try out a remote development kit in real time.
Memory support ranges from 4 to 8 kbytes of RAM and up to 64 kbytes for single-cycle flash. The 10-bit analog-to-digital converter (ADC) supports up to eight channels. A channel sequencer that lets designers prioritize inputs accepts triggers from a range of inputs, including one of many analog comparators, reducing software overhead.
The chip has up to 36 general-purpose I/Os (GPIOs) that are shared with the other peripherals, including up to two UARTs, SSI, and I2C ports. One big difference between these new chips and chips from some competitors is that Luminary Micro does not share I/O pins among peripherals, only GPIO, so all options are available to developers. All of the pins can be used for interrupts. Interrupt response time is six to 12 cycles.
The chips have JTAG support, including access to all I/O pins, not just debug and flash access. The timers target motor control. An enhanced motion control subsystem is an option. The chips also can manage dead-time. And, the system includes quadrature encoder support.
Pricing for the chips starts at $3.96. The top-end 50-MHz LM3S828 with 64 Mbytes of flash costs $5.47. The chips come in 48-pin low-profile quadflat packages (LQFPs).