The rise of high-speed 8-bit network MCU - Embedded.com

The rise of high-speed 8-bit network MCU

The evolution of the Internet began in the early of 1970's with theARPANET project by the US Department of Defense to make thecommunication between different computer systems possible. In the1980's, the academic world and universities began to participate in thedevelopment, using LAN (local area network) as a means to share dataand files between different computers.

By the 1990's, corporations and businesses began to operate underthe World Wide Web (WWW), and online users increased dramatically withemail and e-commerce as significant driving forces.

The ensuing Internet era will augment the computer-to-computernetworks of the 1980's and the user-to-user networks of the 1990's withInternet capable devices, resulting in the rise of M2M communication and the so-called “Ubiquitous Network Society.”

The microcontroller used in embeddedsystem design is primarily focused on control capabilities, whereintegration is the primary objective. Based on the target application,chip designers will incorporate different degrees of memory,input/output interface, and computational ability into a singlecontroller.

Generally, microcontrollers integrate a variety of serial orparallel peripheral interfaces with GPIO (general purpose input/output)capabilities. Serial interfaces include UART, SPI , I2C, Microwire and1-wire.

The parallel interface is linked to other chips using an externalmemory interface (EMI), local bus interface (LBI), or PCI businterface. A microcontroller can be configured to be a Slave host, atwhich point any other controller configured as Master host cancommunicate to the Slave using a conventional 8/16-bit parallelinterface. The timing functions can be achieved through a watchdogtimer, timers/counters, programmable counter array (PCA), or areal-time clock(RTC).

The inclusion of other interfaces depends on specific applications.For example, speech channel applications build in I2S, AC'97, SP/DIF orother speech codecs. Consumer electronics build in USB, USB OTG, LCDcontrollers/drivers, and possibly include MMC or SD memory cardinterfaces.

Battery or module controllers build in SMBus, industrial automationapplications build in CAN controllers, automobile data communicationsbuild in CAN/LIN controllers. LAN applications use network controllerswith built-in 10/100Mbits Ethernet MAC/PHY. Figure 1 below depicts the8-bit network network-capable microcontroller discussed in this articleand it's I/O interface and applications.

Figure-1Application diagram of High-speed 8-bit network MCU

Based on its ease of use, low cost, high bandwidth, stability,security, and compatibility across devices, Ethernet has become the defacto standard of network access.

Today, Ethernet has surpassed the use of both SOHO and enterprisenetworks and expanded into consumer electronics, gradually becoming themost attractive solution for embedded systems to access the network.

With the growth of home networking, media sharing, and the gradualprevalence of hi-definition content, the expansion of high bandwidthEthernet connections to other non-PC devices in the home is also on therise. In addition, the stability and security of Ethernet makes it anattractive solution for more industrial applications as well.

The proliferation of M2M communications anticipates a rise inEthernet-capable microcontroller market. Ethernet can be applied toinclude a broad range of products, from household appliances, factoryand industrial automation, security systems, remote surveillance andmanagement, environmental observation, remote data accumulation, andother applications.

In recent years, the market for microcontrollers has shifted awayfrom consumer electronics to data/telecommunications, resulting inincreased demand of high-powered 32-bit microcontrollers for advancedproducts.

However, as the prices of 8-bit microcontrollers have plateaued andbegun to decrease, they have been singled out as the low cost solutionfor M2M and networking devices. How does one increase the performanceof the 8-bit controller? How does one increase the network bandwidth?The question of how to achieve a high level of integration yetmaintaining the cost-cutting and miniaturization demands of the marketare the key issues facing today's chip designers.Embedded Ethernet Solution
There are four primary forms of embedded Ethernet designs (see Figure 2 below ). Scenario (I) andScenario (II) feature a microcontroller without an integrated networkcontroller, and are able to interface with an external networkcontroller through a serial (i.e. USB host) or parallel (i.e. PCI ornon-PCI local bus) interface.

Scenario (III) and (IV) feature an integrated Ethernet/networkcontroller and microcontroller; in particular, Scenario (IV) involvesthe highest degree of chip integration. Also, the form factor for theembedded Ethernet system design is getting smaller with each successivegeneration. This contributes to lowering the total cost of the system(i.e. eliminating PCB components costs, chip material costs) and powerconsumption.

The right panel in Figure 2 depictstwo possible solutions for achieving a small form factor. Top rightdepicts a small chip package using a non-PCI Ethernet controller with64-pin connector to achieve a form factor that is about one-fourth thesize of a US dime. Bottom right achieves a high level of integration,featuring a network capable microcontroller combining 10/100MbitsEthernet PHY, MAC, TCP/IP accelerator, and integrated flash, decreasingthe physical size of the total package significantly.

Figure-2Embedded Ethernet SolutionFigure-2 Embedded Ethernet Solution

Embedded Ethernet Microcontrollertechnological advances
An alternative approach to embedded Ethernet development is to observethe trend of integrating networking microcontrollers into the so-calledsingle chip SoC (System on Chip) solution. This progression can bedivided into four levels (see Figure3 below ).

The first level has a relatively low degree of integration,requiring an external flash memory and a non-PCI local bus to connectto the Ethernet controller; this creates a three-chip solution. Thesecond level integrates flash to the microcontroller, but stillrequires a non-PCI bus to connect to the Ethernet controller; thiscreates a two-chip solution.

The third level combines the microcontroller, flash memory, and theEthernet MAC layer into a single chip, which then connects to anexternal PHY; this creates also a two-chip solution. The fourth andideal outcome combines the microcontroller, flash memory, and both theMAC and PHY layers in a single-chip solution, creating both the chipwith the broadest and most comprehensive applications and the smallestform factor in the market.

Figure-3Embedded Network Evolution

As the semiconductor process technology has advanced, the standardsfor microcontroller performance in operation timing and machine cyclehave also increased. The Machine Cycle is defined as the process ofexecuting a complete instruction within the microcontroller. Shorteningthe machine cycle speeds up the execution of the instruction.

When Intel announced the first generation of the 8051microcontroller in the 1980's, the standard operation timing wasclocked at 12Mhz. Every twelve clock cycles constitutes a machinecycle, or so-called 12T, and the majority of 8051 instructions can beexecuted in one or two machine cycles. The operation timing of latergenerations of 8051-compatible microcontrollers has been upgraded tosupport 16/24/33/40/60MHz clock speeds, and machine cycles have beenshortened to 4T/2T as well.

Breakthroughs in chip design technology today have made possibleoperation timing speeds of up to 100MHz, and the newest generation ofthe 8051 microcontroller performs at 1T, or Single Cycle instruction.The acceleration of both the operation timing and machine cycle createsa multiplicative effect that creates exponential increases in the totalperformance with speeds running up to 100MIPS. The microcontroller in Figure 1 earlier is an example ofsuch a chip.

The program memory of the original 8051 microcontroller was 4kB;this was gradually upgraded to support up to 8/16/32kB and reached anupper limit of 64kB. Subsequently, using “Bank Select” technology toswitch between two sets of 64kB, engineers were able to break the limitand support up to 128kB.

The data memory of a conventional 8051 is 128B; this was alsogradually upgraded to support up to 256/512/1k/2k/8kB. Upgrading boththe program memory and data memory were essential as microcontrollerbecame controllers for memory and resource intensive tasks such asTCP/IP and embedded web server.

In the past, the clients tended to select 32-bit high-end networkcontroller SoC's due to higher density requirement on both program anddata memory in their applications. This class of network controllerusually supported program and data memory up to 256kB and 32kBrespectively, and used an external bus interface to expand memory ifnecessary.

Today, designers have the option to use a low-cost 8-bit network SoCcontroller. For example, the 8051 compatible network microcontroller80390 has no limitation on the memory addressing and can support up to16MB of program memory, large enough to support TCP/IP and embedded Webserver applications. The central panel in Figure-1 depicts this designwith an 8051/80390 processor core with an embedded flash size of 512kBand 32kB of data memory.

Also, unlike Mask ROM or One Time Programmable (OTP) ROM, whosefirmware cannot be modified after shipment, the integration of flash inthe network microcontroller makes field upgrades possible throughEthernet and UART. This not only speed up the development process, butmakes it easier to patch or upgrade the firmware at a later time.Increasing Network Throughput throughHardware
In addition to increasing the memory size, clock rate, and reducingmachine cycle to improve the performance of the core processor ofnetwork controller, there are also hardware mechanisms to relieve thecomputing power of the processor such as TCP/IP Accelerator and DMA (Direct Memory Access). Inthe header of IP or TCP, there is a column labeled as header/packetdata checksum.

This checksum is a mathematical algorithm to ensure the integrity ofpacket during the transmission on the network. Network controllersnormally use a software program to process TCP/IP protocol, but thecomputation of the checksum requires a great deal of computer powerfrom the processor and may degrade the network performance (see Figure 4 below ).

Figure-4Ethernet packet format and the location of header checksum

The hardware enabled TCP/IP Accelerator can offload microcontrollercomputer power and improve the network performance. Also, the processof TCP/IP packets involves mass data transfer between hosts. Thehardware-enabled DMA moves the data within memory blocks without goingthrough the read-write cycle from the main processor to further improvethe system performance.

The applications of Network MCUs
The overall performance improvement in the 8-bit networkmicrocontroller makes it an attractive cost down alternative to the32-bit microcontroller for embedded applications. Applications thatonce required a 32-bit microcontroller can now be powered by the lowercost, highly integrated and higher capacity of 8-bit networkmicrocontrollers.

This includes a number of growing applications including homeappliances, factory/building automation, industrial equipments,security systems, remote control/monitoring, and streaming mediaapplications such as POS terminals, vending machines, IP camera,Internet radio, automatic meter reading, environmental monitoringsystems, network sensors, networked UPS, Serial to Ethernet adapter,and Ethernet to ZigBee bridge, etc.

The following section details three of the applications mentionedabove: network cameras, serial servers, and Ethernet to ZigBee bridges.

Network (IP)Cameras. Network, or IP (Internet Protocol) cameras are rapidlybecoming a common gadget in today's digital home or business. A networkcamera offers users the ability to conduct remote monitoring andmanagement at any given time and place through the simplicity of theInternet and a web browser. The two most common formats used today forimage compression are Motion JPEG and MPEG4. Due to the bandwidthlimitation in broadband services today, there is trade-off between theimage resolution and transmission speed.

The advantage of Motion JPEG solution is its low cost; due to itslow compression rate, it requires less power from the hardware. Thebudget network camera is an ideal give-away promotion item for bothbroadband and mobile phone service providers. Typical uses of networkcameras include surveillance, remote monitoring of children, thein/outflow of shop entrances, no-man factory/warehouse, etc.

With an 8-bit high performance network microcontroller and MotionJPEG codec, one can design and build a low cost network camera withvideo and audio as well as Pan/Tilt functionalities (see Figure 5 below ).

Figure-5Dual mode Ethernet/USB network camera

Serial Servers. As information technology advances, more and more automation equipmentsin the factory are connected into the Internet. The main purpose ofserial server is to transmit data between serial ports (RS-232/485/422)and Ethernet, allowing users to access, monitor and manage theequipment or device with these serial interfaces through the Internetremotely.

The applications cover both industrial and commercial uses includingmedical equipments, electronics billboards, PLC, Machine-HumanInterface and barcode scanners, etc. With an 8-bit high performancenetwork microcontroller, one can design and build a serial server withan appropriate serial interface as depicted in Figure 6 below . This can shrink thesize of both the PCB and the system, making the design process easierand cheaper as well as replacing multi-chips solutions in the markettoday.

Figure-6Single chip solution for RS-232 to Ethernet application

Ethernet toZigBee bridges. Many vendors are promoting WirelessSensor Network products with the strong emergence and industryacceptance of the 802.15.4/ZigBee standard. The applications of thisnew wireless network technology include both industrial and homeautomation such as digital home appliance control, security monitoring,goods control, home-care, etc.

As ZigBee proliferates in the factory and the digital home,controlling and managing these equipments and devices embedded withZigBee becomes an issue. With a 8-bit high performance networkmicrocontroller with SPI interface and 802.15.4/ZigBee controller, onecan design and build a compact Ethernet to ZigBee bridge as depicted inFigure 7 below .

Once this compact Ethernet to Zigbee bridge is connected to a HomeGateway, the Home Gateway will become a dual role device (Home gatewayand Zigbee Gateway), allowing the user to control and manage any ZigBeedevice through remote Internet access.

Figure-7Ethernet to ZigBee Bridge

The 8-bit network MCU's Future inthe Market
The technological advances in 8-bit microcontrollers have allowed thesehighly integrated and low cost solutions to reach into the market onceaccessible only by 32-bit controllers.

With the growth of Machine-to-Machine communication and a risingnumber of Internet-ready devices, the market for high capacity networkcontrollers are likely to experience heightened demand in theforeseeable future. The role of the 8-bit network microcontroller willlikely be an important one in powering future embedded systems in themarketplace.

Jason Wang is director ofMarketing at ASIX Electronics. He can be reached at jasonw@asix.com.tw.Harvey Jan is director of R&D. He can be reached atharvey@asix.com.tw.

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