Texas Instruments' (TI) continues to push its Arm Cortex processors. It's latest 80MHz LM4Fx Stellaris ARM Cortex-M4F floating-point microcontroller (Fig. 1) takes advantage of TI's 65nm technology. It is an interesting complement to TI's recent 100 MHz DSP (see Fixed-Point DSP Delivers For Less Than $2) that comes in under $2. The LM4Fx Stellaris line starts around $1.50 and targets mobile applications as well as industrial automation and motion control applications.
Mobile and battery operated applications will benefit from the low standby currents. The chips can sip as little as 1.6µA. The real time clock (RTC) pushes this up to only 1.7µA. Wakeup time is under 500µS. Even in active mode the chip only draws 30mA.
The microcontrollers incorporate the StellarisWare ROM that contains device firmware for routines such as motor control. This is handy for the optional motor control PWM with dual quadrature encoders. StellarisWare shows up in other Stellaris microcontrollers providing a compatible, cross platform runtime. The ROM can also reduces flash storage requirements.
The flash storage for the line tops out at 256 Kbytes with up to 32 Kbytes of SRAM. There is 2 Kbytes of EEPROM implemented via flash with an interrupt-based asynchronous write. It also supports a secure boot feature.
The analog peripherals include dual 12-bit analog-to-digital converters (ADCs) that operate up to 1 Msample/s. There are three comparators as well.
Communication is where the Cortex-M4 often has advantages over DSPs. The LM4Fx Stellaris includes USB with support for host, device and On-The-Go USB. The chips also have UARTs, I2C, SSI/SPI and CAN interfaces.
The LM4F232 evaluation kit (Fig. 2) is priced at $149. It has a 96 by 64 pixel color OLED display. Debugging is provided by an on-board USB interface. It comes with TI's Code Compuser Studio. The kit and the Stellaris product line are supported by a wide range of third party IDEs and development tools.