Microcontrollers target automotive passive-keyless-entry

Microchip Technology's latest flash, 8-bit PIC microcontroller—featuring a 3-channel transponder analog front end and the company's integrated KEELOQ cryptographic peripheral and nanoWatt low-power consumption technology—is geared for automotive passive-keyless-entry (PKE) and other wireless authentication applications.

Designers of such automotive and wireless security systems require integrated communication, security, and reliable low-power operation. The new PIC16F639 microcontroller meets these needs by providing automotive electronics engineers with the 3-channel low-frequency transponder analog front end (see below), KEELOQ, nanoWatt Technology, and the compute power of a PIC microcontroller in a small 20-pin SSOP package.

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The three-channel transponder analog front end provides bi-directional LF communication, commonly used in PKE and RFID applications. KEELOQ technology is based on a proprietary, non-linear encryption algorithm that creates a unique transmission on every use, rendering code capture and resend schemes useless.

The analog front end is the key enabler for PKE, notes Willie Fitzgerald, director of marketing for Microchip's Automotive Products Group. “The availability of the three channels minimizes miscommunications, due to antenna orientation, and the fact that these channels can be individually enabled or disabled.” The analog input sensitivity and input modulation depth sensitivity are key parameters of the analog front end. With the input sensitivity being typically 3 mVpp, (and as low as 1 mVpp) the range of the system is about 2.5 meters, which allows most automotive applications. “With input modulation depth sensitivity up to 12%, analog front end delivers the highest modulation depth sensitivity available in the marketplace today,” claims Fitzgerald. He adds the programmable wake-up filter is a key element to support the low-current consumption requirements. “This wake-up filter allows the MCU to remain in sleep mode until a 'valid' input signal is detected by the analog front end.”

Integration issues
In designing the PIC16F639 Microchip engineers optimized the degree of integration between the MCU and the analog front end for performance, flexibility, and maintaining a small footprint. A dual-die/single-package approach was chosen. This architecture supports future migrations to different MCUs, based on the application requirements. The two functional dice are internally bonded via an SPI interface.

“The integration challenges were significant,” notes Fitzgerald. “Achieving high input sensitivity while maintaining low current consumption is critical for PKE systems, because this parameter impacts the communication range. Several current-saving mechanisms, including programmable wake-up filter, 16 msec soft inactivity timer, channel enable/disable, etc, were developed to support extended battery life. With the high modulation depth sensitivity, detection of a low-level amplitude modulated signal in a noisy environment is enabled.”

Applications for the PIC16F639 include: Automotive (PKE, tire-pressure monitoring systems); authentication (intelligent RFID, property and identity, hospital systems, computer access); and security systems (door locks, gate openers, doggie or pet doors, remote sensors, and their intercommunication).

Additional key features of the microcontroller include:

  • Precision 8 MHz internal oscillator with software clock switching
  • Up to 3.5 kbytes of flash program memory
  • 128 bytes of RAM
  • 256 bytes of EEPROM
  • Two analog comparators
  • An 8-bit timer and a 16-bit timer

    LF analog front end features include:

  • Three channels for omni-directional 125 kHz wireless communications
  • Three mV input sensitivity
  • Programmable antenna tuning
  • Support of batteryless operation

    Low-power and reliability features include:

  • Ultra-low power wakeup (ULPW)
  • Software-selectable brownout reset (BOR)
  • Programmable low-voltage detect (PLVD)
  • Wakeup reset (WUR)
  • Enhanced watchdog timer (EWDT)

    Tools, Availability and Pricing
    The PIC16F639 is supported by Microchip development tools, including: MPLAB Integrated Development Environment (IDE); MPLAB ICE 2000 in-circuit emulator; MPLAB PM3 universal device programmer; PICSTART Plus low-cost development system; MPLAB ICD 2 in-circuit debugger/programmer; and the new PICkit 2 Starter Kit (expected to be available in August). In addition, a complete PIC16F639-based Passive Keyless Entry Reference Design (part # APGRD001) is expected to be available in the third quarter of this year.

    The new PIC microcontroller is sampling, and volume production is expected in Q3 2005. In 10,000-unit quantities, the PIC16F639 is $2.18 each. For additional information

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