Manipulating Digital Patterns With a New Binary Sequence Generator

Fnou srupty BErNG A MATHEMATIcAL cuRroslry fifteen years ago, binary sequence generating shift registers have become important tools in a surprising range of applications. The random-like patterns of 1's and 0's generated by these circuits are used to obtain increased range in radars,' to encode and decode digital and analog data for secure storage and transmission,2 to encode and decode digital messages for error-free transmissions,3 to simulate digital data for system tests, and to generate random numbers for Markov simulation studies.n To meet an incipient demand for test instruments capable of generating pseudorandom binary sequences, a binary output was included in the Hewlett-Packard Model 3722A Noise Generator, introduced in 1967.u The binary output is a two-level waveform that switches levels in synchronisrn with regularly-occurring clock pulses. Switching does not occur on every clock pulse, however, but on a random-like selection of clock pulses that give the waveform nearly ideal statistical characteristics. The fact that the sequences can be repeated, though, means that the sequences are pseudorandom. More recently, HP introduced the l925Au and 8006A Word Generators. These generate 16-and 32-bit words for de-bugging circuits with known short words but can also generate pseudorandom binary sequences for simulating digital data streams. Increased Flexibility Now, because of the widening applications for this kind of instrument, a new Pseudo-Random Binary Sequence (PRBS) Generator (Model 19304) has been designed. A /+-width module for the HP 1900-series Pulse Generators (Fig. 1), this instrument is the first to give the operator complete control over the feedback configuration in the sequence-generating shift register, making possible more than a million difierent sequences, some 73,000 of them being maximal length sequences. Another first-time capability: the new PRBS generator can process digital sequences as well as generate them. For example, it can encode and decode externally-gen-Cover: Model 1930A Pseudo Random Binary Sequence Generator, a new addition to the 19??-series pulse-processing modules, contributes both a tesf paf-tern and a means of detecting errors rn tests of digital t r ansm ission system q u al ity. The most tlexible binary sequence generator yet ottered in a commercial instrument, it can also encode and decode digital messages, and generate random-like sequences of l's and 0's. erated data streams. It can also compare an externally-generated data stream with its own internally-generated replica to detect differences between the two (Fig. 2). For sequential comparisons and decoding, a new method Fig.2. Model 19304 generates etrct …