From: "Noddy" Newsgroups: comp.arch.fpga Subject: Open collector outputs Date: Tue, 4 Sep 2001 09:45:08 +0200 Organization: Rhodes University, Grahamstown, South Africa Lines: 16 Message-ID: <999589294.992902@turtle.ru.ac.za> NNTP-Posting-Host: turtle.ru.ac.za X-Trace: hippo.ru.ac.za 999589295 59504 146.231.128.8 (4 Sep 2001 07:41:35 GMT) X-Complaints-To: abuse@ru.ac.za NNTP-Posting-Date: Tue, 4 Sep 2001 07:41:35 +0000 (UTC) X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 Cache-Post-Path: turtle.ru.ac.za!phat@big-ears.phys.ru.ac.za X-Cache: nntpcache 2.4.0b2 (see http://www.nntpcache.org/) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.ifi.unizh.ch!news.imp.ch!news.imp.ch!fr.clara.net!heighliner.fr.clara.net!news.tele.dk!small.news.tele.dk!212.74.64.35!colt.net!dispose.news.demon.net!demon!btnet-peer0!btnet!ctb-nntp1.saix.net!quagga.ru.ac.za!not-for-mail Xref: chonsp.franklin.ch comp.arch.fpga:9698 Hi, Can anyone tell me the quickest way to make an output on the Spartan XL (3.3V) open collector. I read in the documentation that you can use a tri-state buffer, but the method doesn't make sense to me. It says tie the tri-state pin to the output, and tie the input to ground. If the input pin is to ground, where doesn my input signal go? To the tri-state pin? Anyway, there must be another way to configure the pin to opn-collector... I just can't find it as of yet. Thanks Adrian ###### From: Philip Freidin Newsgroups: comp.arch.fpga Subject: Re: Open collector outputs Organization: Fliptronics Reply-To: philip@fliptronics.com Message-ID: <6g29pt8rij3e2rddkq75phutl084dnv5re@4ax.com> References: <999589294.992902@turtle.ru.ac.za> X-Newsreader: Forte Agent 1.8/32.548 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 49 Date: Tue, 04 Sep 2001 01:11:58 -0700 NNTP-Posting-Host: 216.103.85.188 X-Complaints-To: abuse@pacbell.net X-Trace: news.pacbell.net 999591135 216.103.85.188 (Tue, 04 Sep 2001 01:12:15 PDT) NNTP-Posting-Date: Tue, 04 Sep 2001 01:12:15 PDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.ifi.unizh.ch!news.imp.ch!news.imp.ch!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed.wirehub.nl!63.208.208.142.MISMATCH!feed1.onemain.com!cyclone-sf.pbi.net!206.13.28.33!news.pacbell.net.POSTED!not-for-mail Xref: chonsp.franklin.ch comp.arch.fpga:9719 There is a tri-stateable buffer in the output cell (IOB) It has three signals: "in", "out", "tri-state control". The "in" pin is driven by FPGA stuff The "tri-state control" pin is driven by FPGA stuff The "out" pin connect to an external pin of the FPGA You have a signal that you want to go off-chip, as an open collector siglal (when logic low, drives low, when logic high, does not drive, and relies on an external pullup circuit (resistor for example) to establish a logic high. Connect your output signal to the "tri-state control" pin of the output buffer Connect the "in" pin of the output buffer to ground (0, low) The "out" pin of the output buffer is already connected to the package pin. When your output signal is low, in enables the buffer, so it drives the "out" pin low, because the "in" pin is low. When your output signal is high, the buffer is tri-stated, and the output level is determined by external factors. The on-chip pullup resistors are not appropriate for open-collector type pullup. You need an external resistor with a value probably below 2000 ohms. ("tri-state" is a registered trade mark of National Semiconductor ) Philip On Tue, 4 Sep 2001 09:45:08 +0200, "Noddy" wrote: >Hi, > >Can anyone tell me the quickest way to make an output on the Spartan XL >(3.3V) open collector. I read in the documentation that you can use a >tri-state buffer, but the method doesn't make sense to me. It says tie the >tri-state pin to the output, and tie the input to ground. If the input pin >is to ground, where doesn my input signal go? To the tri-state pin? > >Anyway, there must be another way to configure the pin to opn-collector... I >just can't find it as of yet. > >Thanks >Adrian > > Philip Freidin Fliptronics ###### Message-ID: <3B94BB3E.A54D3A42@andraka.com> From: Ray Andraka Organization: Andraka Consulting Group, Inc X-Mailer: Mozilla 4.77 [en] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: comp.arch.fpga Subject: Re: Open collector outputs References: <999589294.992902@turtle.ru.ac.za> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 31 Date: Tue, 04 Sep 2001 11:27:19 GMT NNTP-Posting-Host: 24.13.238.93 X-Complaints-To: abuse@home.net X-Trace: news1.wwck1.ri.home.com 999602839 24.13.238.93 (Tue, 04 Sep 2001 04:27:19 PDT) NNTP-Posting-Date: Tue, 04 Sep 2001 04:27:19 PDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.ifi.unizh.ch!31955!news.imp.ch!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newshub2.home.com!news.home.com!news1.wwck1.ri.home.com.POSTED!not-for-mail Xref: chonsp.franklin.ch comp.arch.fpga:9687 T<= input signal I<= gnd O<= output That way When the input signal is active (obuft is active low input, obufe is active high input) the outputdrives to ground, when inactive it is hi-Z. Noddy wrote: > Hi, > > Can anyone tell me the quickest way to make an output on the Spartan XL > (3.3V) open collector. I read in the documentation that you can use a > tri-state buffer, but the method doesn't make sense to me. It says tie the > tri-state pin to the output, and tie the input to ground. If the input pin > is to ground, where doesn my input signal go? To the tri-state pin? > > Anyway, there must be another way to configure the pin to opn-collector... I > just can't find it as of yet. > > Thanks > Adrian -- -Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 email ray@andraka.com http://www.andraka.com