X-Authentication-Warning: delorie.com: mailnull set sender to djgpp-bounces using -f From: "Matthew Smith" Newsgroups: comp.os.msdos.djgpp Subject: Re: TSR to run 60Hz CGA at 50Hz Date: Mon, 11 Feb 2002 07:38:38 -0000 Lines: 45 Message-ID: References: <3C66FEB7 DOT 396324D0 AT anywhere DOT com> NNTP-Posting-Host: modem-3200.rhino.dialup.pol.co.uk X-Trace: news7.svr.pol.co.uk 1013413011 19713 62.137.108.128 (11 Feb 2002 07:36:51 GMT) NNTP-Posting-Date: 11 Feb 2002 07:36:51 GMT X-Complaints-To: abuse AT theplanet DOT net X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4522.1200 To: djgpp AT delorie DOT com DJ-Gateway: from newsgroup comp.os.msdos.djgpp Reply-To: djgpp AT delorie DOT com "noLCDpanels" wrote in message news:3C66FEB7 DOT 396324D0 AT anywhere DOT com... > > No this post hasn't been lost for 10 years. I have an 8-bit CGA with > > composite out that I wish to use for debugging with RHIDE/DJGPP. I > > have fitted a b/w modulator to the card but the signal is 60Hz and my > > UK TV can't handle this. Does anyone have a TSR or something which > > will set the output to 50Hz and keep it there ? > > Is that a *real* CGA display adapter? If so, you might be out of luck. > The display-adapters of this era (early 1980s) had a fixed set of > clock circuits, to produce all dot clocks. If the card happens to > support a 50Hz scanrate, you might be able to set it through the CGA > BIOS. If not, you'd probably have to desolder one of the CGA board's > clock generators, and replace it with a different value (X * 5/6) The dot clock is fixed (well, on this card it is switchable to MDA mode too) but the horizontal and and vertical sync are generated by the 6845 chip according to the values set in the registers. These are very like the VGA registers but at a different port address. The dot clock for 60Hz video is very similar to 50Hz video, as the horizontal rates are 15360Hz and 15625Hz. This meagrly causes the picture to shifted off-centre and is not a serious problem. I can probably write a simple TSR to switch the mode myself, but I'm looking for a robust TSR which can survive all the mode switching that Windows, RHIDE, and a DJGPP/Allegro program will do. I suspect the best answer is to find an MDA monitor from somewhere, or get an eprom programmer and fix the CGA bios, but I have a TV sitting here doing nothing already. I actually have a dual-head Matrox G400 installed too. I bought that specifically for dual-screen debugging but was disappointed to find the drivers do not emulate CGA/MDA on the second output. Matrox are not interested in this dwindling market :(