HP 37717C Operating Manual page 29

HP 37717C PDH / DSn Features
Binary Interfaces. Option UH3 (US7)
The binary clock and data input
thresholds and polarity are selectable.
The DATA threshold selections are:
TTL (1.5V), ECL (-1.3V) and GND
(0V)
The CLOCK thresholds are as for data
plus AUTO (mean signal level).
The CLOCK and DATA polarity may be
normal or inverted.
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