ENGINEERING FEATURE

Micros, Micros Everywhere

Microcontrollers represent a remarkable continuing success story: everyday experience is enough to tell us that. Just when it seems that every possible use for a microcontroller must have been exhausted, someone comes up with yet another application.

As a consequence, and despite some expectations to the contrary, the diversity of chips available has continued to increase. The advent of lower cost 16-bit and 32-bit devices has not, as some predicted, meant an end to the market for 8-bit controllers: Flash versions have supplemented mask-programmable and RAM-based versions, not supplanted them; and increasing levels of integration have not produced an appreciable trend towards a fully-equipped, one size fits all product.

Examples of these seemingly infinite variations are most evident in the market for processors based on the ARM core. Vendors such as Analog Devices, Atmel, Freescale, NXP, STMicroelectronics and Texas Instruments all produce such core-based devices: but each component has its own range of features and benefits that make it suitable for very particular applications.

The ARM core is now widely acknowledged as the most widely deployed processor in the history of electronics. Its rise has coincided with the growth in portable appliances that can use its features of low power and small memory footprint. Meanwhile, ARM’s overall market approach has created a community of users who understand the architecture; a correspondingly deep fund of legacy code, which those users are very keen to re-use; and a rich set of third-party design support tools and operating system software aimed both at existing and new users.

ARM7-Based Devices

The ARM7 core is often viewed as the industry's standard core architecture, and forms the basis of microcontrollers from Atmel, NXP, STMicroelectronics and Texas Instruments (TI). The latter’s TMS470 family of microcontrollers, for instance, targets automotive applications requiring a balance of the high performance offered by a 32-bit RISC with 16-bit code density. The TMS470 microcontroller integrates Flash or Read-Only Memory (ROM) and intelligent peripherals for embedded systems, including a flexible timing coprocessor, 10-bit analogue-to-digital converter, multiplex communication modules, watchdog and serial interfaces.

Atmel is another ARM supporter, and the company recently announced three new additions to its SAM7 family of USB-equipped MCUs. These include an External Bus Interface (EBI), providing access to over a Gigabyte of data storage space, in the form of NAND Flash, SDRAM, CompactFlash, SRAM or ROM.

Atmel’s aim with the SAM7E series is to enable portable data logging applications, for instance medical monitoring, without the need to use a more powerful controller. The devices provide a complementary Error Correcting Code Controller (ECC) that compensates for data lost by Flash over time; and security features to keep both data and code safe from theft.


Figure 1 – Atmel SAM Microcontrollers

Amongst NXP’s most recent ARM7 offerings are two communications-oriented devices, the NXP LPC2300 and LPC2400. These feature two AHB buses, enabling simultaneous operation of Ethernet, USB (On-The-Go and Host), CAN, SDRAM and other peripherals.

The two buses are complemented by three independent Direct Memory Access engines, allowing the devices to be used in applications such as industrial networking, infotainment, consumer and medical devices, and Point-of-Sale equipment. The new devices also include a Real Time Clock (RTC) with 2KByte of battery back-up SRAM, which allows the RTC to continue running even when the chip's power is shut down.


Figure 2 – NXP LPC23xx ARM7 Device

Illustrating the variety that is attainable by building on a single core, STMicroelectronics’ ARM7-based STR750F family includes some 30 different derivatives. Able to support full-spec operation at both 3.3V and 5V, the devices provide outstanding low power modes down to 12µA in STOP or 10µA in STANDBY modes. Fast startup and Automatic Wake Up (AWU) capabilities enhance the usefulness of such modes.

The STR750F family is equipped with Flash memory capacities from 64Kbyte up to 256Kbyte, plus an additional 16Kbyte bank of Read-While-Write Flash for EEPROM emulation. Its extended feature set includes a backup clock that starts operating if the main clock fails, a particularly attractive feature for security applications such as alarm system control panels and vending machines.


Figure 3 – Block Diagram of STMicroelectronics STR750F

ARM9-Based Devices

ARM9-based devices provide more processing power, higher data throughputs, and via an integrated MMU, enhanced support for embedded operating systems. Atmel’s recently announced AT91SAM9263, for instance, includes a 200MIPS ARM926EJ-STM-based core. To achieve on-chip data transfer rates of up to 41.6Gbit/s it also integrates 27 DMA channels including a proprietary 18-channel Peripheral DMA Controller (PDC); a 9-layer bus matrix; and two additional busses for Tightly Coupled Memories (TCMs).

Primarily designed for use in graphically interfaced, data-intensive applications such as networked medical monitoring equipment and GPS navigation systems, the device includes an on-chip camera interface, a TFT/STN LCD controller, and audio and hardware-based graphics processing. Mirroring the approach taken in the SAM7E, the AT91SAM9263 includes two EBIs. This eliminates the need for the LCD controller and CPU to share memory, and can increase available CPU MIPS by 40%.


Figure 4 – Block Diagram of Atmel AT91SAM9263

NXP’s ARM9 offering is spearheaded by the LPC3180, which includes a vector floating-point co-processor and integrated USB On-The-Go, as well as the ability to operate in ultra-low-power mode down to 0.9V. The chip is intended for a wide range of high-precision applications such as Point-of-Sale (PoS) equipment, medical and industrial devices, Global Positioning Systems (GPS), and robotics.

The floating-point unit speeds up typical calculations by a factor of four to five in scalar mode and much more in optimised vector mode, according to NXP. The USB Host/OTG capability allows direct connection to PDAs, smart-card readers and printers, supplementing an array of peripherals that includes seven UARTs, SPI, I²C, RTC with a separate power domain, NAND Flash, and DDR memory controllers.


Figure 5 – NXP LPC3180 ARM9 Offering

A recent addition to the STMicroelectronics ARM9 range is the STR91X Flash-based series. With a 96MHz internal clock and burst-mode Flash memory interface, the devices can deliver 96MIPS direct from Flash. When combined with the ARM9’s ability to perform single-cycle DSP instructions, this makes the chips a good choice for speech processing, audio algorithms, and low-end imaging applications.

Emphasising the device’s familiarity and ease of design, STMicroelectronics says that code is binary-compatible with existing ARM7 software.

STR91X devices integrate a 10/100 Ethernet MAC with DMA and MII port, 2.0B active CAN bus interface and full-speed (12Mbit/s) USB. The communications line-up is completed by three 16550-style UARTs with IrDA protocol; two fast (400kHz) I²C interfaces; two channels for SPI, SSI or Microwire; and an optional 8/16-bit EMI bus.


Figure 6 – STMicrolelectronics STR91X Devices

Micros/Precision Analogue Combination

Analog Devices takes a slightly different approach in its use of processor cores: reflecting the company’s heritage in handling linear functions, its MicroConverter family combines precision analogue circuitry with an industry standard microcontroller and Flash memory.

Its ADuC7000 series integrates an ARM7TDMI core, and includes application-specific products such as the recently announced ADuC703x precision automotive battery controller. With up to three 16-bit ADCs, a Local Interconnect Network (LIN) transceiver, embedded Flash memory, and on-chip PGA (Programmable Gain Amplifier), attenuation resistors and temperature sensing, the ADuC703x replaces several devices.

Other ARM7-based application-specific offerings from Analog Devices include a single-chip energy meter, and the ADuC7128 device optimised for motor control applications.

In addition to its ARM-based offerings, Analog Devices also produces a range of products utilising the 8052 core, another de-facto industry standard. This family includes fourteen variants with feature sets including high-precision, multi-channel DACs/ADCs and PWM generation. The ADuC848, for instance, is optimised for applications in industrial control, smart sensors, loadcells and instrumentation that require precision acquisition of multiple (up to 10) channels.

Proprietary Architectures

Despite the rapid rise of core-based devices, more traditional eight-, 16- and 32-bit processors remain undimmed in popularity. For example, Atmel’s AVR® family of 8-bit microcontrollers have a RISC core running single cycle instructions and a well-defined I/O structure that limits the need for external components. Internal oscillators, timers, UART, SPI, pull-up resistors, pulse width modulation, ADC, analogue comparator and watchdog timers are some of the features offered by the AVR range. Furthermore, AVR instructions are tuned to decrease the size of the program whether the code is written in C or Assembly. With on-chip in-system programmable Flash and EEPROM, the AVR is ideal for designers looking to optimise cost and get product to the market quickly.

Atmel has also created processors specifically for 21st century applications that require both performance and low power consumption. The AVR32 32-bit RISC processor core is designed to do more processing per clock cycle so the same throughput can be achieved at a lower clock frequency. This means the compute-intensive algorithms required for today's applications can be executed with substantially less power consumption.

The AP7000 is the first AVR32-based processor family and the first to integrate on a single chip, virtually all the functionalities required for multimedia systems deployed in cell phones, digital cameras, PDAs, automotive infotainment, set top boxes, and home entertainment systems, as well as network switches/routers and printers.


Figure 7 – The Atmel AVR32 32-bit RISC Microcontroller

Renesas argues that 16-bit devices remain a valid choice in the middle ground of performance, offering a balance of CPU and memory capabilities, peripherals, pin-count and usability to meet the majority of applications. Most applications cannot afford unnecessary costs, whether that is in the price of the MCU itself, or in the penalty of extra board area, layout traces, power consumption or EMI.

To allow designers to choose whatever they feel is the best fit for their applications, Renesas offers devices for 8- to 32-bit applications that are core-compatible, code-compatible, peripheral-compatible, tool and even pin-compatible. This means that designers can base a platform on one MCU but can substitute an alternative, compatible part on to the PCB to give either higher or lower performance as required.


Figure 8 – Renesas Offers a Full Range of 8-bit, 16-bit and 32-bit Devices

The approach is exemplified by the company’s recent announcement of new compatible controllers at the low-cost and high-performance points of its range. The R8C/2x 16-bit controllers are supplied in packages with 20, 32, 48 and 52 pins, and are suitable for ultra-low-power and battery applications, with current consumption as low as 0.8µA in wait mode.

For high-performance applications, the M32C/87 controllers are application-optimised consumer and industrial products designed to efficiently implement code written in the C language. They exhibit high performance in terms of EMS (ElectroMagnetic Susceptibility), low EMI (Electro Magnetic Interference) and low power consumption.

NEC Electronics is another microcontroller manufacturer offering a variety of 8-bit, 16-bit and 32-bit devices. Used mainly for very small devices and targeted at cost-sensitive applications, the 78K0 core is NEC’s mainstream 8-bit core. The newest addition to the 78K family is the 16-bit 78K0R core. It is also based on the 78K0 but, thanks to its 16-bit-wide databus and 16-bit-wide ALU, provides real 16-bit performance. In the 32-bit space NEC offers devices based on its V850ES and V850E1/E2 cores. The V850ES is optimised for lowest costs, making it an ideal choice for applications often served by 16-bit microcontrollers. To complement this, the V850E1 core is designed for high performance, with its successor, the V850E2, pushing the performance bar even further.


Figure 9 – NEC Microcontrollers

Toshiba also continues to offer an enormous range of products, aimed every conceivable application, with 8-bit, 16-bit and 32-bit CPUs. Its recently-announced TMP92CZ26, for example, is based on its TLCS-900/H1 high-speed 32-bit CISC core and is intended for Man-Machine-Interface (MMI) applications.

Featuring an integrated VGA LCD controller and full-speed USB Controller, the device was originally designed for use in PDAs, but is now available more widely for deployment in equipment as diverse as weighing scales and PoS terminals. It allows the display of complex information via a colour screen, with the ability to add a touch-screen interface.

Toshiba also continues to offer 16-bit devices, including the TMP91FY42FG, which integrates 256Kbytes of on-board Flash and a comprehensive range of peripherals. Based on the company's ultra-low-power TLCS-900/L1 processor core, the device will operate with voltages of between 2.7V and 3.6V: three standby modes, including a programmable IDLE option, reduce overall power consumption.


Figure 10 – Toshiba's TMP91FY42FG

The device provides rapid context switching, and includes a high-speed, four-channel micro-DMA and powerful bit manipulation and arithmetic instructions. Toshiba’s SuperFlash implementation provides fast programming and three distinct programming modes for both pre- and post-production programming flexibility.

Whilst also continuing to offer 8-bit, 16-bit and 32-bit options, Freescale is particularly focused on providing designers with a seamless migration path from 8-bit to 32-bit devices. The company’s controller continuum concept is a roadmap of pin-compatible 8-bit and 32-bit devices with shared peripherals and a common set of tools.

The starting point for this roadmap is the RS08 ultra-low-end core, designed for traditional electro-mechanical designs that require additional functionality. The RS08 is a simplified version of Freescale’s high-performance, low-power HCS08 architecture, requiring 30% less silicon area.

The core features a condensed instruction set, allowing compact and efficient coding of most embedded applications with less than 16KByte of Flash memory. Tiny and short addressing modes allow more efficient access and manipulation of commonly used variables and registers, whilst a shadow program counter facilitates more efficient subroutine calls.

For designs that can use the power of a 32-bit processor, Freescale provides pin-compatible entry-level ColdFire V1-based microcontrollers with connectivity and security features for cost-sensitive applications. The continuum continues through Coldfire V2-, V3- and V4-based devices.

Also a part of the continuum are continued enhancements to the CodeWarrior Development Studio with automatic code generation; and a unified hardware development platform that will provide common board and cable interfaces across architectures. The tool set is intended to make programming the 32-bit 68K/ColdFire architecture as simple and straightforward as programming an 8-bit microcontroller.


Figure 11 – Freescale Controller Continuum Concept

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