[time-nuts] Z3805 utility, Was: AW: (no subject)

Robert Benward rbenward at verizon.net
Mon May 24 12:27:34 UTC 2010


Bob,

I just went out an ordered a bunch of gender changers and null modem cables, and a DB9 tester (with a NM switch!).  I 
started doing the same as you, using a sharpie to mark my cable.

An update, the unit has been running overnight, the holdover light is on, but nothing else.  I still suspect the RS-232 
is dead.  I now have to suspect my other antenna as well.  It was good when pulled out of service, but who knows.  I 
wish I had my old Garmin 45 with the external antenna.  I also ordered an RS-422 adapter.  I'm hoping I can connect with 
that.

Bob

----- Original Message ----- 
From: "Bob Camp" <lists at rtty.us>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Monday, May 24, 2010 7:15 AM
Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)


> Hi
>
> Gotta label them *something* or sorting through them in the cable bin becomes pretty difficult.
>
> In addition to the wiring options you can (obviously) have either a male or female on either end. There are so many 
> "odd" pieces of gear out there that you can have pretty much any combination.
>
> Bob
>
>
> On May 23, 2010, at 11:22 PM, Robert Benward wrote:
>
>> My experience with the term "straight through" is that I've seen RS-232 cable that have the ground pin connected to 
>> the shell.  In a "straight through" the pins are one to one and the only thing connected to the shell would be the 
>> shield if one is available.
>>
>> Bob
>>
>> ----- Original Message ----- From: "Bob Camp" <lists at rtty.us>
>> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
>> Sent: Sunday, May 23, 2010 9:21 PM
>> Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)
>>
>>
>>> Hi
>>>
>>> Long ago I decided to go with the terms "straight" and "null modem" for the cables I use. NM and ST are easy to mark 
>>> and hard to confuse.
>>>
>>> Bob
>>>
>>>
>>> On May 23, 2010, at 8:58 PM, jimlux wrote:
>>>
>>>> Stanley Reynolds wrote:
>>>>
>>>>> <snip>
>>>>> Dec computers / terminal servers were as I described, but many brands
>>>>> were different. Still have a BOB aka break out box with LEDs to
>>>>> indicate levels, matching transmit and receive is easy, getting the
>>>>> hardware flow control / signaling right was a little more difficult.
>>>>> straight cable = pin to pin
>>>>> crossed cable = null modem = swapped pins
>>>>> The phrase "null modem" comes from no modems or the configuration
>>>>> that allows two singular ports to be connected, this cable would
>>>>> cross the receive and transmit pins, and some would call it a cross
>>>>> over cable. A null modem cable would be used to connect two computers
>>>>> together and a program like kermit used to transfer files.
>>>>
>>>>
>>>> Yep.. DTE cable to DCE communications medium(phoneline) DCE to DTE
>>>> DCE == Modem (e.g. a Bell 202 or 212, for instance)
>>>>
>>>> There were the flow control (RTS/CTS) used to turn around a half duplex link.  And, there are also the secondary 
>>>> transmit and receive (for a low rate reverse channel).  If you were receiving data from the link (DCE), you'd 
>>>> assert RTS, and when the modem had switched, it would tell you CTS, and off you'd go.  (fancy modems used the 
>>>> reverse channel to send the request to the far end, which would acknowledge... others just use a fixed time delay) 
>>>> There are also pins for the clock (since some of these modems were used on synchronous data links).
>>>>
>>>> the "crossover" occured in the DCE to DCE link (that is, you'd transmit from one DCE to the other DCE's 
>>>> receiver)...
>>>>
>>>> the nominal cable between DTE and DCE was straight through. With no real convention on male/female.. most devices 
>>>> had female sockets, and the cables usually were male male plugs.  IBM PCs had male on the chassis for DTE, as did 
>>>> some PDT-110 (VT-100/LSI-11 smart terminals), but most other terminals (the LSI ADM-x, Hazeltines, etc.) all seemed 
>>>> to have female, as did the TI 800 series printer/terminals.
>>>>
>>>> So, a "null modem" was a cable that emulated the DCE to DCE connection..
>>>>
>>>> there are/were various strategies on how sophisticated the reverse is.. do you also send the secondary channel? 
>>>> What about clocks? Most folks ignored all that and used RTS/CTS
>>>>
>>>> Or you strap RTS to CTS on your side, the other side does the same.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> I think the phrase "standard cable" which could be null or straight
>>>>> depending on the use  is the confusing part.
>>>>> Phone cables RJ11 and RJ45 swap the wires which is standard.  Network
>>>>> cables match the wires with the same color always on the right which
>>>>> is standard. But even when a phone cable is standard it is not
>>>>> interchangeable with a standard network cable. Again we have a need
>>>>> for cross as well as straight network cables.
>>>>
>>>>
>>>> And, to make things worse, there are different "pair" arrangements.
>>>>
>>>>
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>>>
>>>
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>
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