Communication Protocol

Motorola FLEX Protocol References

I've been working on a project involving the Motorola FLEX paging protocol. There is plenty of useful information out there about implementing the FLEX protocol. Strangely enough, in the age of modern search engines I could not easily find many of these resources. Because of our struggle to

Table of Contents:

  1. About FLEX
  2. FLEX Patents
  3. Useful Resources
  4. Open-Source Projects
  5. Our Observations

About FLEX

If you need an introduction to FLEX, start here for basic information:

FLEX Patents

The following patents are helpful for understanding the FLEX protocol in detail:

  • US5555183 - describes the FLEX messaging structure and frame collapsing
  • US5168493 - describes the signalling protocol for sending FLEX transmissions

Useful Resources

These were the most helpful documents for implementing a FLEX decoder:

Open-Source Projects

These projects can serve as useful references if you run into a problem decoding FLEX messages:

Our Observations

The long capcode decoding scheme described in the patent is incorrect. The conversion scheme described in the ARIB standard seems to be what is actually used by our test equipment. The actual conversion scheme that worked for us is:

#define LONG_CAPCODE_CONVERSION 2068480 // Patent says: 2067456, but that math doesn't work

uint32_t rawAddrToLongCapcode(uint32_t addr1, uint32_t addr2)
    uint32_t addr2_complement = (uint32_t)~addr2;
    // We have to truncate because we have bit 0x80000000 set and it shouldn't be
    return (((addr2_complement << 15) + LONG_CAPCODE_CONVERSION + addr1) & 0x7FFFFFFF);