[time-nuts] Re: Lpfrs-10 serial port failure

[Steve Hendrix, P.E.]

It's possible the logic levels are inverted. Standard RS-232 is a 
positive voltage for a 0, negative for a 1, whereas most TTL level 
interfaces use 5V for 1, 0V for 0. Although it doesn't fully meet the 
spec, sometimes interfaces are built using TTL to directly interface to 
RS-232, counting on the fact that most "RS-232" interfaces actually 
tolerate a transition level somewhat positive of ground. Your 
description of detecting a Break condition suggests that you need to 
invert the signals.

Steve Hendrix

On 2025-11-21 1:34 AM, Bryan _ via time-nuts wrote:
> Hmm, looked at the manual available online and it appears your settings are correct. I did see this note, but don't see a schematic to the referenced adapter circuit in the manual.
>
> IMPORTANT NOTE In most cases, the serial PC interface accepts the 0 to 5V level and a direct connection can be made. In case this 0 to 5V standard is not working , please refer to the small adaptation circuit called ‘ RS 232 adapter circuit’ described in annex I.
>
> -=Bryan=-
> ________________________________
> From: HB9DRI, Alex Artieda via time-nuts <time-nuts at lists.febo.com>
> Sent: November 20, 2025 9:40 AM
> To: 'Discussion of precise time and frequency measurement' <time-nuts at lists.febo.com>
> Cc: hb9dri at bluewin.ch <hb9dri at bluewin.ch>
> Subject: [time-nuts] Re: Lpfrs-10 serial port failure
>
> Hello Brian
>
> I have no idea with the previous owner, I follow what the manual said:
>
> The data transfer from the LPFRS can be made by direct connection to a PC or
> standard terminal.
> The data transfer parameters are the following:
>
> bit rate: 1200 bits
> parity: none
> start bit: 1
> data bits: 8
> stop bit: 1
>
> My device is flag as TTL means logical levels 0 to 5vdc following standar
> logic, some information in internet spoke about (RS232, TTL) but the label
> on my device spoke just TTL, a pure RS-232 will involve positive and
> negative voltages.
>
> I try with puTTy, RealTerm, and Hyperterminal, configure echo, just a
> important observation in RealTerm when connect the device the Terminal said
> (BREAK CONDITION DETECTED) and the Led BREAK is RED.
>
> I assume the serial interface is damage, that is the reason of my post.
>
> 73 de Alex, HB9DRI
>
> -----Original Message-----
> From: Bryan _ via time-nuts <time-nuts at lists.febo.com>
> Sent: Thursday, 20 November 2025 17:20
> To: Discussion of precise time and frequency measurement
> <time-nuts at lists.febo.com>
> Cc: Bryan _ <bpl521 at outlook.com>
> Subject: [time-nuts] Re: Lpfrs-10 serial port failure
>
> Did the unit work before when connecting via serial. What protocol are you
> using to connect via serial.
>
> -=Bryan=-
> ________________________________
> From: HB9DRI, Alex Artieda via time-nuts <time-nuts at lists.febo.com>
> Sent: November 19, 2025 11:52 PM
> To: time-nuts at lists.febo.com <time-nuts at lists.febo.com>
> Cc: HB9DRI, Alex Artieda <hb9dri at bluewin.ch>
> Subject: [time-nuts] Lpfrs-10 serial port failure
>
> Dear friendsIm totally new in this list, looking for a solution to a problem
> with my Lpfrs-01.I had this unit second hand, in optical an funtional
> pristine condition , take only 3min to lock. All looks good except I cannot
> connect to the serial port, the device specified TTL Rx and TX in the lable,
> no response at all when send M, when is connected to a USB uaart converter
> and I send M the TX line show a permanent 3.6vdc and a train of pulses show
> up in the oscilloscope, at the same time the DXine is clamp to 1.4vdc and
> nothinig appears, suspect the serial interface buffer is damage.I will
> apprecite some advice to repair the unit, I try tl fk d a diagram with no
> success, only few tier down photos, maybe some body can point me where I xan
> sfart looking, maybe a IC to replace.Any help is welcome.73 de Alex,
> HB9DRISent from my Galaxy _______________________________________________
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