As a general convention in Eurorack, clock pulses are +5v, but not vpp as clocks (and gates and triggers) are only positive-going from 0v. There are negative-going trigger/gates out there, but they're unusual, such as Behringer's use of the VERY EFFING ANNOYING Moog S-Trig standard in some of their Moog-alikes, or the various modules that invert the clock for synths that use that, such as the Korg MS-20. That adherence to the +5v standard is what allows you to run that module, clock an internal sequencer by some other manufacturer, send gates through Boolean logic, etc and have the whole mess work together...it's been that way since Dieter Doepfer came up with Ye Olde Eurorack Standard about 25-ish years ago.