Out in Front: March 28, 1996

The impetus behind the Flex paging protocol comes from high speed, noise immunity, and power savings. The high speed (as fast as 6400 bps vs the 1200 or 2400 bps typical of other protocols) is due to four-level FSK transmissions, compared to other protocols’ two-level FSK. Increased noise immunity is due largely to data interleaving and sophisticated error correction. Power savings result from Flex’s synchronous nature; a pager needs to "wake up" for only a second or so in each four-minute interval. Extensions of the Flex protocol also add two-way and voice paging capabilities (see "Not your ordinary beepers: New pagers add two-way and voice features," EDN, Dec 21, 1995, pg 65).

Flex’s features require complex processing, which the new paging ICs provide. The MC68175 processes information that has been received and demodulated from a radio paging channel, selecting only those messages addressed to its host pager and passing them on to the pager’s µC (Figure 1). The MC68175’s tasks include reconstructing data from interleaved transmissions, applying error correction, and controlling timing and power sequencing (Figure 2). The MC68175 will be available in samples and small quantities next month and in production quantities later this year. It will cost less than $7 (100,000).
—by Gary Legg

Motorola Inc, Schaumburg, IL. (847) 413-2515

Texas Instruments Inc, Dallas, TX. (214) 480-4546.