Date: Wed, 7 Jul 1999 22:20:11 +0200 (SAT) From: John Hay <jhay@mikom.csir.co.za> To: davids@webmaster.com (David Schwartz) Cc: jhay@mikom.csir.co.za (John Hay), stable@FreeBSD.ORG Subject: Re: PPS API change assert/clear Message-ID: <199907072020.WAA06678@zibbi.mikom.csir.co.za> In-Reply-To: <000401bec8b1$12fba1c0$021d85d1@youwant.to> from David Schwartz at "Jul 7, 1999 12:44:06 pm"
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Uhm, did you measure it? I just connected a modem through a breakout box so that I can easily measure the voltages. At the start the DCD voltage is -12V and after it has connected with carrier I have 7.5V. That seems like a negative to positive transition for assert? I was actually the one that started the discussion on the PPSAPI mail list because I was also under the impression that RS232 signals are active low. But after a lot of talking and some measurements we found that it isn't true. Maybe you can think of it as active low if you measure between the serial chip and the RS232 driver chip, but that is the only place where it is active low according to my measurements. John -- John Hay -- John.Hay@mikom.csir.co.za > > > Do you mean that if you measure the voltage on the DCD pin and it go from > > negative to positive (ASSERT) you get a CLEAR from the software? > > Negative to positive is not an assertion of DCD. DCD is active low. It has > been logically asserted when the voltage goes negative. > > > That is > > wrong and not what I see here. Do you have version 1.224.2.6 of sio.c? > > I know it has been broken in versions before that in stable and versions > > before 1.246 in current. > > Why is that wrong? (I know, the standard says so, but it seems to me that > the standard makes no sense.) > > When I asked Ulrich Windl, one of the authors of the standard, (but this > may be before the clarification), he said: > > Me: Since DCD is active-low, is an 'ASSERT' a high-to-low transition on the > DCD pin? > > Ulrich: This problem has been discussed a lot. ASSERT is from the > perspective > of the UART's register. ASSERT means the CD bit in the modem status > register has been set. Depending what your line drivers and level > converters do, the level may change. > > Ulrich gave me the answer that I expected. The one that I thought made > sense. And the Linux PPSkit that Ulrich Windl wrote works as he stated. > > It's hard for me to keep my software working when the definition keeps > changing. :/ > > David Schwartz > http://www.gpsclock.com/ > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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