The schematic shows 33 Ohm series resistors on the logic-outputs. That's probably dimensioned to get about 50 Ohm output impedance. Last I tried an octoclock, driving a 50 Ohm load gives about a 2.5 V amplitude pulse. This is from 2016-09, but maybe the schematic hasn't changed since that.
[image: image.png] On Fri, Jun 11, 2021 at 5:00 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 06/11/2021 09:45 AM, Jim Palladino wrote: > > Hi Marcus, > > Right -- the output of the Octoclock is 5V. I'm not seeing how the N320 > can accept that as an input. The knowledge base article says the N320 > expects 5Vpp at the 1pps input. But the schematics/parts data sheet for the > input buffer don't seem to support that . . . unless I'm missing something. > > Thanks, > Jim > > It certainly looks like a potential problem, but I haven't heard of anyone > having 1PPS failure issues on the N320 when used with > Octoclock--pretty sure it was tested with Octoclock prior to release. > But I'll check with R&D. > > > > ------------------------------ > *From:* Marcus D. Leech <patchvonbr...@gmail.com> > <patchvonbr...@gmail.com> > *Sent:* Friday, June 11, 2021 9:39 AM > *To:* usrp-users@lists.ettus.com <usrp-users@lists.ettus.com> > <usrp-users@lists.ettus.com> > *Subject:* [USRP-users] Re: N320 1PPS input voltage > > On 06/11/2021 09:11 AM, Marcus Müller wrote: > > Hello Jim, > > > > > > hm, that knowledge base article must be wrong: The octoclock internally > only has a 3.3V > > supply. But before I say something wrong here, let me check back. > > > > > > Best regards, > > > > Marcus > The 1PPS outputs on the Octoclock are bufered by 7404 inverters, which > appear to have a 5V Vcc. > > > > > > > On 11.06.21 14:17, Jim Palladino wrote: > > > >> Hello, > >> > >> We are planning on using an octoclock with several devices, including > an N320. The > >> octoclock outputs a 5V 1pps signal, but I'm confused about the N320 > 1pps input. > >> > >> According to ( > https://urldefense.proofpoint.com/v2/url?u=https-3A__kb.ettus.com_N320_N321-29-3A&d=DwIF-g&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=XUEEtUEfpaAEGxRI-WGuqHauOvsPdD2NZkfwDnwpYx0&m=-9vS_HYCWF4BKKIX7QR3SO2LJ3yD1MyEElYsX5a8WMs&s=TdFHQJNItGehIsL1D4yXezIfq_vO05AvF1_lMSyNpHs&e= > >> "PPS - Pulse Per Second Using a PPS signal for timestamp > synchronization requires a > >> square wave signal with the following a 5Vpp amplitude." > >> > >> If I look at the schematics for the N320, on page 15, > >> ( > https://urldefense.proofpoint.com/v2/url?u=https-3A__kb.ettus.com_images_f_f4_USRP-5FN3XX-5FMB-5FSchematic.pdf&d=DwIF-g&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=XUEEtUEfpaAEGxRI-WGuqHauOvsPdD2NZkfwDnwpYx0&m=-9vS_HYCWF4BKKIX7QR3SO2LJ3yD1MyEElYsX5a8WMs&s=6JTHdP9IoYFRQhn24LgJjEofkuFwgAsHTs9iHhgMuBg&e=) > they show that the input > >> 1pps signal goes through an NC7SV157. Vcc for that is 3.3V in the > schematics. > >> > >> According to the datasheet, the absolute maximum rating on the input is > 4.3V. > >> " > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.onsemi.com_pdf_datasheet_nc7sv157-2Dd.pdf&d=DwIF-g&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=XUEEtUEfpaAEGxRI-WGuqHauOvsPdD2NZkfwDnwpYx0&m=-9vS_HYCWF4BKKIX7QR3SO2LJ3yD1MyEElYsX5a8WMs&s=XPmiCDRDfM2wVtI1g4KChC9dkOJhMyrqBTMv_Rx01Xg&e= > " > >> > >> So, I'm not sure how the N320 can safely accept a 5V input (from the > octoclock or other > >> device). > >> > >> Thanks, > >> Jim > >> > >> > >> _______________________________________________ > >> USRP-users mailing list -- usrp-users@lists.ettus.com > >> To unsubscribe send an email to usrp-users-le...@lists.ettus.com > > _______________________________________________ > > USRP-users mailing list -- usrp-users@lists.ettus.com > > To unsubscribe send an email to usrp-users-le...@lists.ettus.com > _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com > > > _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com >
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