Electronic Design

"Arm"-ing Analog Microcontrollers

Analog Devices moves the 32-bit ARM7 core where 8-bit analog-enabled MCUs once tread.

Standard Arm-based products are quickly becoming the standard for midrange microcontrollers (MCUs). Analog Devices' ADuC702x family puts these products in the middle of analog space. It's not surprising, given Analog's previous endeavors with its 8052-based, single-cycle, 8-bit ADuC8xx MCU family.

The company went beyond just wrapping the 32-bit, 45-MHz, single-cycle ARM7TDMI core with the same devices found in the ADuC8xx family. It listened to embedded developers and added a programmable logic array (PLA) to minimize a project's bill of materials (BoM).

Some analog peripherals not found in most other Arm-based MCUs are found on the new MCUs. For instance, there are four 12-bit digital-to-analog converters (DACs). Fronting the 12-bit analog-to-digital converter (ADC) is a 12-channel multiplexer. There's an uncommitted comparator as well.

The ADuC702x's digital complement is equally strong. Among the four serial links are two serial peripheral interfaces, an I2C, and a UART. The chip has up to 40 general-purpose I/O (GPIO) ports, depending upon the device. Four 16-bit timers are available in addition to three pulse-width-modulation (PWM) timers. The PWMs can be combined into a three-phase PWM with both true and inverted outputs. This makes the device suitable for a variety of different types of motor-control applications.

On-chip memory consists of 8 kbytes of SRAM and up to 62 kbytes of flash memory. Applications can run out of the faster SRAM or flash memory. SRAM delivers single-cycle instruction execution speed.

The MCU features a power-supply monitor for brownout detection as well as an on-chip oscillator. The oscillator will drive the processor at speeds of up to 35 MHz. Its accuracy is within 2%. A phase-locked loop (PLL) keeps things running even if the external clock stops the system from switching to the internal clock. An external clock is required to run at speeds up to the 45-MHz limit.

The ADuC702x can be a power miser. It consumes less than 2 mA/MHz, and it draws well under 100 mA even when running at full speed. Additionally, support is included for a wide range of power-down modes. When combined with these power-down modes, the PLA can deliver more sophisticated power management.

Because it's configurable, the PLA allows for dynamic reconfiguration. Inputs and outputs can be linked to most internal and external connections. For example, a PLA output can reset the chip, start an ADC acquisition, or wake up the chip when it's asleep. Although the PLA lacks the power of a larger FPGA, it's more than sufficient to replace the simple logic that often surrounds an otherwise single-chip solution.

The family supports gang programmers in addition to serial flash downloads. At 115 kbits/s, the interface can program 62 kbytes of flash in under 10 seconds.

Most Arm-based MCU vendors have opted to make a low-cost development kit available to developers. Although this trend is leading to less expensive Arm development tools in general, it may take a while before solutions over $1000 disappear.

The $249 QuickStart Development System from Analog Devices includes a suite of software-development tools by KEIL Software and IAR Systems—the Keil "ULINK" JTAG emulator and an evaluation board. Keil µVision3 IDE includes a compiler, simulator, and debugger. The debugger is limited to applications smaller than 16 kbytes. The IAR Systems package includes a similar complement of tools. Analog Devices also features a graphical PLA design tool that generates C code.

Pricing for the ADuC70x family starts at $4.55, while the full-feature ADuC7026 with 62 kbytes of flash tops out at $12.80. The small 40-pin version is only 6 by 6 mm. CAN support will be available in the future.

Analog Devices Inc.

  • 45-MHz 32-bit ARM7 TDMI
          T - 16-bit Thumb instruction set
          D - on-chip debug (JTAG)
          M - multiply and multiply/accumulate
          I - in-circuit emulation support
  • Memory
  • 8-kbyte SRAM (program and data)
  • 62-kbyte flash memory
  • Analog I/O
  • 12-channel, 12-bit 1-MHz ADC
  • Quad 12-bit DAC
  • 20-ppm/°C VREF, +3°C temperature sensor
  • Uncommitted comparator
  • Digital I/O
  • Programmable logic array
  • Four timers
  • Serial: two SPI, one I2C, UART
  • Up to 40 GPIO
  • Three-phase PWM or three individual PWMs
  • Packaging
  • 40-pin 6- by 6- to 9- by 9-mm LFCSP package
  • Temperature range −40°C to 85°C, 105°C, or 125°C
  • 3-V operation, uses less than 2 mA/MHz

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