Motorola uses expertise to develop 8bit MCUs to boost -

Motorola uses expertise to develop 8bit MCUs to boost


Colin Holland takes a look at the first six members of Motorola'sNitron family of lower cost 8-bit microcontrollers that looks towiden the company's penetration outside automotive applications.

Motorola's Nitron series of six small-profile, 68HC08-based Flash8-bit MCUs are available in 8- and 16-lead packaging and priced toextend the company's market reach in to lower cost applications.

Targeted at consumer electronics, industrial and automotivesystems, the company's advances in manufacturing technology and highproduction volumes will provide the devices down to $0.70US withplanned future derivatives under $0.50. This pricing level will allowthe MCUs to compete against others with on-chip one-time programmable(OTP) memory, and in some cases, read only memory (ROM).

Also aimed at cutting costs, Motorola is making available freedevelopment tools – valued at more than $2,000 – for the Nitron FlashMCUs.

The Nitron (68HC908QT and 68HC908QY) family includes six devices.As well as the 68HC08 central processing unit (CPU), they includein-application and in-circuit re-programmable Flash memory (1.5K to4K bytes), and a number of on-chip peripherals.

These include a two channel 16-bit timer system with selectablecapture, compare and pulse width modulation (PWM), system protectionsuch as selectable trip point low voltage inhibit (LVI) andauto-wakeup from STOP COP (Computer Operating Properly). A fourchannel 8-bit analog to digital converter (ADC) is included on theQT2/QT4/QY2/QY4 versions.

Nitron microcontroller family device schematic

In-application and in-circuit re-programmable, programming timesare as fast as 32µs/byte. Block protection and security featureswill help customers guard intellectual property contained in softwarecode. They allow embedded system designers to program late in themanufacturing cycle, make upgrades remotely in the field, and toquickly respond to the changing needs of their customers and themarket with more flexibility than one-time programmable and ROM-basedMCUs.

Available packages include 8-lead PDIP, 8-lead SOIC, 16-lead PDIP,16-lead SOIC, and 16-lead TSSOP. The 16-pin TSSOP package offers 14I/O pins in less PC board area than the 8-pin packages. Parts in8-pin packages offer a 6-pin I/O port where each pin can beconfigured for use with on-chip peripheral systems, system functions,or general purpose I/O. The 16-pin packages offer a second 8-bitgeneral purpose I/O port.

Oscillator options include an internal trimmed oscillator thatneeds no external connections or components, an R-C option that usesone external connection and an external resistor to set thefrequency, a standard external crystal option which uses two externalpins, or an external oscillator option which uses one pin to connectan external clock source. The internal oscillator reduces system costand reduces board space while eliminating the EMI that is generatedfrom external clocks.

On-chip peripheral functions include a full-featured 2-channel16-bit timer system and a 6-pin keyboard interrupt system.

Application programs can use some pages of FLASH memory as EEPROMwhile using the rest for program memory. System integration functionsare also fully supported by the on-chip power-on reset (POR), COPwatchdog, and low-voltage-inhibit (LVI) circuitry.

Based on the 68HC08 architecture, an extension of the 68HC05architecture that has existed for more than 20 years, the Nitronproducts feature a CPU that allows efficient, compact modular codingin assembly or C language.

The efficient instruction set includes multiply and divide while16 flexible addressing modes include stack relative with 16bit stackpointer.

The 4 channel, 8-bit ADC provides conversion in 17µs andeases interfacing to analog inputs such as sensors.

There are up to 13 bi-directional I/Os and one input. These highcurrent I/Os allow direct drive of LED and other circuits,eliminating external drivers and cutting system cost. The keyboardscan with programmable pull-ups removes the need for external gluelogic when interfacing to simple keypads.

The low-voltage inhibit with selectable trip points improves thereliability by resetting the MCU when voltage drops below the trippoint.

The Timer Interface Module on the 908QT microcontrollers is commonto all of the HC08 Family. It has the capability to perform multiplechannels of input capture, output compare or pulse width modulated(PWM) output, with a resolution down to 125ns.

This is a powerful feature rarely found on a microcontroller ofthis size, and can be used to provide much faster and more accuratetiming functions than can be achieved using software routines, aswell as greatly simplifying development.

The 908QY devices provide a similar set of features, but in avariety of 16-pin packages. A tiny 16-pin TSSOP package allows up to14 pins to be used as inputs or outputs, while occupying a space lessthan 35mm2.

Development support is taken from the larger M68HC08 devices andincludes a monitor ROM and an on-chip breakpoint module. The monitorROM supports traditional MON08 monitor mode and includes utilityroutines for programming and erasing the on-chip FLASH memory.

Monitor mode was developed as a feature of the M68HC08 MCUarchitecture to provide basic in-circuit debugging, as well asprogramming of nonvolatile memories.

Monitor mode is not a substitute for full chip emulation, but itallows a low-cost connection to a host computer, which sends commandsserially to the MCU. These commands perform read and write operationson the MCU's registers and memory. The system developer does not haveto be concerned about the monitor commands since these are embeddedin the programming/debugging tools.

However, there are some practical limitations that must beconsidered when designing a system that will be programmed ordebugged in-circuit using monitor mode.

Monitor mode uses a single I/O pin to communicate with a host PC.This pin is controlled by the monitor mode firmware in the MCU. Thepin is switched between input and output as it emulates the serialprotocol to the PC. This limitation only applies during monitor mode.As soon as the chip is released from monitor mode, the pin reverts toits I/O function.

Monitor mode must have a clock frequency that will allow the MCUto match the serial baud rate of the PC. In most cases the debugconnector can provide a clock signal that can overdrive the crystalon the target board.

The Metrowerks CodeWarrior Development Studio Special Edition forthe 68HC908QT/QY family is available at no charge to registered usersof Motorola's web site and contains tools from several vendors.

It includes an optimized 68HC908QT/QY Family C compiler,assembler, debugger, simulator, flash programmer, and an auto-codegenerator for on-chip peripherals.

A special-edition evaluation board that features a battery powered68HC908QT4 device, LEDs, potentiometer, push button, access to allI/O for user-provided interfacing, a software demo and applicationcode.

The board includes an 8-pin plastic DIP device that ispre-programmed with a monitor access program and a smalldemonstration program. The monitor access program allows the board tobe interfaced to a host personal computer (PC) for debug and FLASHprogramming operations.

The small demonstration program shows how to use the timer, A toD, and keyboard interrupt functions of the microcontroller.

A voltage regulator is included to provide 5V to the MCU from a 9Vtransistor battery. An RS232 level shifter and a DB9 connector areincluded to interface the evaluation board to the serial port of aPC. A single MCU pin is used to communicate with the host PC at astandard 9600 baud rate. A potentiometer is connected to an A to Dpin, a pushbutton switch is connected to a keyboard interrupt pin,and an LED is connected to a general purpose output pin so a smallapplication program can demonstrate these on-chip systems.

A CD is provided which includes complete documentation,application notes, and development software. A complete CodeWarriordevelopment environment is included along with FLASH programmingtools, an M68HC08 assembler, and a C compiler (memory size limited to4Kbytes which is the size of the FLASH memory in the Nitron seriesparts.

Third-party programmers such as the Cyclone stand-alone programmerfrom P&E Microcomputer Systems can measure the on-chip oscillatorfrequency in the application system and program a trim adjustmentfactor into the FLASH memory. Depending on the oscillator optionused, these MCUs can operate at up to 32MHz.

Motorola also offers 68HC08 Web-based training as part of a rangeof services that are designed to make it easy for customers todesign-in and use the microcontrollers.

Market provides opportunities for 8-bit MCUs withFlash memory

According to specialist market researchers, SEMICO, Motorola wasthe top seller of 8bit MCUs in 2001 with 24% of the total worldmarket. In 2002 sales of 8-bit MCUs are expected to grow 4.4% withanother jump of 12.2% in 2003, partly achieved by taking market shareform the 4-bit MCU sector.

SEMICO believes that the 8bit devices need to address a broadmarket requirement with a large number of peripheral configurationsfor specific market needs. While automotive and consumer applicationsdrive the market there is an increasing use of 8-bit devices in ICcards.

At present around 30% of 8bit MCUs have Flash memory, up from justover 20% in 2000, and expected to rise to over 40% by 2005. Atpresent 8-bit MCUs provide 43% of the revenue and 60% of the units ofthe total microcontroller market.

At present nearly two thirds of Motorola's products are used inthe automotive sector but there is a drive to expand the use instandard applications faster to provide equality.

To gain market share, Motorola expects to displace existingsuppliers and capture segment growth to dominate the 8bit market inproliferating low cost applications.

Motorola has shipped more than 5 billion 8bit MCUs since 1993 andalso has several families of 16-bit and 32-bit devices. By 2010 thecompany expects the average person to interact with over 350microcontrollers daily.

Published in Embedded Systems (Europe) November2002

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