Jeff,
Generally for a given DTE, there is a swap of 2&3 when going from DB9 to DB25 and vice-versa. For a normal serial
cable, DTE to DCE, pins 2&3 are swapped. RS-232 states that pin 2 is the TX data, DCE or DTE, on a DB25. It's TX on
pin 3 for a DB9. Therefore to hook a DCE to a DTE, you must swap pins 2&3. The fact that you are going from 2-2 and
3-3 probably means you've inserted a null modem in between, and you are using a standard serial cable.
In the old days... it was a Data Terminal Equipment (DTE) that communicated with Data Communications Equipment (DCE) to
the mainframe. Stanley's assessment is correct, although I'm not sure if the mainframes of yesteryear were DTEs.
A lot of stuff since was designed as DTE, that's why all the trouble these days hooking up all this equipment, there is
no standard as to whether a device should be designed as DTE or DCE.
My PCR-1000s are DCEs, as I use a straight RS-232 cable to hook them up. The manual states the Z3801A is DTE, thus
requiring a null modem in between. That's what you built, when you ran 2-2 and 3-3 between the DB9 and DB25. My DB25
to DB9 adapter has 2&3 swapped. And I know for sure that most DTE in DB9 have male pins. The pins are a quick way to
identify DTE or DCE. On the back of the 3801, the DB25 is female, so like the rest of this spec, it's backwards from
DB9s.
Bob
----- Original Message -----
From: "Stanley Reynolds" <stanley_reyno...@yahoo.com>
To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com>
Sent: Sunday, May 23, 2010 4:56 PM
Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)
----- Original Message ----
From: Jeff Hook <jeffh...@comcast.net>
To: Discussion of precise time and frequency measurement <time-nuts@febo.com>
Sent: Sun, May 23, 2010 12:42:45 PM
Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)
Bob
My 3805 cables look like this
DB9 DB25
2 2
3 3
5 7
(Null Modem)
Jeff
<snip>
straight cable is 2 to 2 to 3 to 3
null modem would be
2 3
3 2
normal usage would be:
terminal (straight cable) modem (phone line) modem (straight cable) computer
computer (straight cable) modem (phone line) modem (straight cable) computer
or if no modems :
terminal (null modem) computer
As has been mentioned many exceptions to the rule.
Stanley
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