Out in Front

Keyless-entry chip set is first with rolling code

Remote-keyless-entry (RKE) systems in cars, home security, and similar applications are convenient but have a weakness: An RF eavesdropper can grab and then retransmit the systems' fixed codes. To prevent such intrusion, Texas Instruments has announced a set of ICs that provides the core of an RKE system that also embeds a self-programming, 40-bit, rolling, or "hopping," code algorithm. Interlopers attempting to tap these systems would find eavesdropping useless, because the key code changes with each use and will never be used again in any practical product lifetime, and the odds of guessing the correct code are approximately one in 4 billion.

The multichannel, advanced-remote-control, serial data transmitter and receiver (MARCSTAR) devices comprise two encoder/decoder ICs, the TRC1300D and TRC1315D. The 1315D has an internal voltage regulator to allow operation from supplies as high as 12V. The encoder/decoder function links to the TRF1400DW tuned-RF (TRF) AM receiver, which contains all needed active circuitry and has –103-dBm sensitivity. The receiver accepts 500-bps to 10-kbps data rates, which the sender transmits as amplitude-shift keying of the carrier (basic on and off modulation). The encoder and decoder cost $0.98 and $1.08 (1000), respectively; the AM receiver costs $1.68 (1000).

By using a SAW device for frequency selection, the 5V TRF receiver requires no tuning or manual adjustment. Also, it produces little radiated RF, because it has no mixer or IF stage, thus making it easier for your design to meet RFI/EMI standards. Although TI designed the initial product for the 315-MHz, US RKE frequency, future designs will accommodate worldwide standards in the 200- to 450-MHz band.—by Bill Schweber

Texas Instruments Inc, Dallas, TX. (800) 477-8924, ext 4500, http://www.ti.com.