Signals & Noise: May 23, 1996

I would like to add the following information to the interesting article, "My memory is not what it used to be: testing RAMs and ROMs," (EDN, Feb 1, 1996, pg 153).

The "nameless" sequence on pg 154 is actually the modified counting-sequence algorithm (Reference 1).

"Counting sequence" refers to the fact that the sequence, when sideways, resembles a binary counter. I first published the sequence, and it was independently publiReferences 2 and 3shed in 1982 (). Maxfield has discovered it for a third time.

The sequence works as follows: An n-wire bus requires [log2(n+1)]+1 patterns, where the equation in brackets denotes the greatest integer function.

Therefore, you can test up to 14 wires with four tests:

00000001111111
00011110000111
01100110011001
10101010101010

The article describes three tests for a five- or six-wire bus:

000111
011001
101010

A seven-wire bus requires four tests, as the article indicates.

Norman Megill
Vice President, Engineering
Production Services Corp
Belmont, MA

Clive "Max" Maxfield replies: I am very grateful to Mr Megill for detailing the history of the modified counting-sequence algorithm (although I am saddened to learn that he discovered and documented it before I did). I will, of course, reference his original paper in any future discussions on this topic.

References

1. Jarwala, N, and CW Yau, "A new framework for analyzing test generation and diagnosis algorithms for wiring interconnects," Proceedings, IEEE International Test Conference, 1989.

2. Megill, ND, "Techniques for reducing pattern count for functional testing," Digest of Papers, IEEE Test Conference, 1979.

3. Goel, P, and MT McMahon, "Electronic chip-in-place test," Proceedings, IEEE International Test Conference, 1982.

Fine-tuning digital-audio broadcasting

I read Dan Strassberg's article, "Digital-audio broadcasting takes to the air" (EDN, Feb 15, 1996, pg 67), with interest. In my position at the National Association of Broadcasters (NAB), I spend much of my time on digital-audio broadcasting (DAB).

A couple of points in the article need clarification. Contrary to what the article states, the ongoing DAB laboratory and field tests are not being conducted "under the auspices of the Federal Communications Commission (FCC)." Also, the National Radio Systems Committee (NRSC) and the Consumer Electronics Manufacturers Association (CEMA) are not "FCC-selected organizations" for implementing these field tests. Rather, the receiver manufacturing and broadcasting industries, through their respective trade associations, the Electronic Industries Association (EIA) and the NAB, initiated these tests.

Next, the FCC did not "decide" to include L-band testing of Eureka, as the article states. The FCC authorized the L-band testing of Eureka as part of the San Francisco field tests in response to requests and as a result of negotiations conducted by the EIA in its role as test manager. In particular, the subcommittees of the EIA and NRSC developed the test plan that includes the EU-147.

Regarding the sidebar, "Just my opinion," Strassberg states that the FCC is "likely to [select] a new-band (NB) terrestrial system that conforms to the European-developed Eureka 147 [system]." I would like to point out that, despite the apparent technical advantages of an NB system, there are serious practical issues that the article does not raise, which make the suggested outcome unlikely.

First, the FCC will not be able to make available spectrum for an NB service, such as Eureka, in the United States—a well-known fact in the DAB community. Second, the Eureka system has some features that are inconsistent with the principles upon which the United States bases its broadcasting. One example is "carrier-sharing," in which a number of broadcaster signals are multiplexed onto a single carrier. For this and other reasons, broadcasters have fully endorsed the in-band approach to DAB, and the FCC will not ignore this endorsement when it comes time to make a decision that will affect the broadcasting community.

My final comment is directed at the exclusion of the NAB in the article. Through the NAB and its radio-broadcasting technical community, the NRSC, US broadcasters have taken an active role in developing DAB. I would encourage your magazine to use the NAB as a resource from which to obtain timely and correct information.

David H Layer
Senior Engineer,
Science and Technology Department
National Association of Broadcasters
Washington, DC

Senior Technical Editor Dan Strassberg replies: The original manuscript did address some of the issues that you raised in your letter. Space limitations precluded including all of the material in the published version, however.