The Tektronix A6701 is an 18-bit Word Recognizer adapter for general purpose oscilloscope triggering. Up to four units may be chained for 72 bits.
Used alone, the max clock rate is 50 MHz.
It requires a separate power supply (015-0356-00) and the matching interconnect cable.
It was introduced in TekScope Vol 11, number 2, July 1979.