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

[Didier Juges]

Bruce,

Thanks for the additional information.

+/- 14V is quite unusually low in my experience. I typically use Maxim parts such as the MAX220 series, which is specified at +/-25V for no damage on the inputs (some parts in that series go to +/-30V).

The bottom line is that as I pointed out earlier, there is no such thing as an RS-232 standard any more.

Didier

------------------------ Sent from my BlackBerry Wireless thingy while I do other things... 

-----Original Message-----
From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Date: Sun, 23 May 2010 10:39:21 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Subject: Re: [time-nuts] Z3805 utility, Was: AW:  (no subject)

Didier Juges wrote:
> Bill, I think you got it backwards. +/- 12V is typical for RS-232, 0/+5V is
> for RS-422 and RS-485.
>
> No RS-232 receiver should be damaged with +/- 12V or even +/- 15V because
> that is their normal operating voltage.
>
> Also, RS-422 and RS-485 have something like 25V common mode tolerance (not
> sure what the actual spec is there,) so that the RS-422 and RS-485 receivers
> should not be damaged by 15V either. The RS-422 drivers are pretty low
> impedance, while the RS-232 drivers are current limited, so I don't think
> that connecting an RS-232 driver into an RS-422 driver will damage either.
>    
Picking one RS485 receiver (ADM1485) at random the receiver absolute 
maximum (no damage) input range is -14V to +14V.
The RS485 receiver operating common mode range is -7V to +12V.
RS422 receivers have an input operating range of -7V to +7V.
The no damage RS422 receiver input ratings may be higher.
> However, most recent (<10 years?) RS-232 receivers will work with a 0/+3V or
> 0/+5V input, conveniently having a threshold a few 10's or 100's of mV above
> ground, even though the original RS-232 spec required receivers that work
> with as low as +/- 3V, and drivers that deliver +/- 9V minimum. Many
> commercial systems use +/- 5V drivers for RS-232 (B&B Electronics sells a
> lot of converters with these voltages). This is a deliciously sloppy spec
> that nobody has met in the last 25 years probably, yet works most of the
> time.
>
> The one thing to avoid is to short an RS-422 (or RS-485) driver to ground,
> as that can actually cause damage, maybe not every time, but definitely not
> recommended. These have relatively high current output capability to drive
> long lines.
>
> Didier KO4BB
>
>
>    
Bruce
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Bill Hawkins
> Sent: Saturday, May 22, 2010 3:09 PM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)
>
> When all else fails, get out the voltmeter.
>
> Do you have power to the antenna? Is it the right voltage? All the way to
> the antenna?
>
> What volts are on pins 2 or 3 relative to pin 7 in the comm connector?
>
> If you see 12 volts, that's RS-422. You may have burned out your computer's
> serial port.
>
> If you see less than 5 volts, that's RS-232 and all should be well, unless
> you see zero volts.
>
> I may have the RS-xxx volts somewhat off because my memory isn't what it
> used to be.
>
> The guy you bought it from should be able to help with comm basics.
>
> Bill Hawkins
>
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Robert Benward
> Sent: Saturday, May 22, 2010 2:08 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)
>
> Hi All,
> I hooked everything up and I still get nothing.  I can't seem to establish
> communications  with the Z3805.  I tried a
> null modem as well, in case the cable (supplied) was wired with the wrong
> connector gender.  I see a green blinking
> light inside, it he left rear corner of the box.  Everything is warm, but
> nothing else.  Any ideas?
>
> Bob
>
>
>
>
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