Re: PET Graphic, Font, 40/80, Composite and Audio Boards

From: Steve Gray <sjgray_at_rogers.com>
Date: Sat, 24 Mar 2018 23:43:19 +0000 (UTC)
Message-ID: <1755503019.439173.1521934999074@mail.yahoo.com>
The first PET models with 9" tube had a fixed 15kHz scan rate which were compatible with NTSC monitors. Later CRTC chip models (ie: 4000, 8000, 8296 and SuperPET with 12" tubes had 20kHz scan rates. The CRTC models can be re-programmed to output 15kHz to be NTSC compatible, or even PAL compatible. 
The 12" monitors themselves have controls to adjust the screen and I have been able to get them to sync to 15kHz but not perfectly. The CBM-II (B-series) machines come in LP and HP models. The LP models have NTSC or PAL output (controlled by a jumper on the board) so are 15kHz roughly. The HP models with internal monitor are 17-18kHz. Yes, the HP does 350 lines.
In terms of scanlines, the CRTC controller has 5 lines (labelled RA0 - RA4) which allows them to have character heights up to 32 lines. It's all programmable. So basically the number of rows and columns and character heights all figure in to what type of video output the system can generate, and what type of monitor is supported. The 6545 CRTC controller is very flexible and was even used in early PC video cards MDA, CGA, EGA and even form the basis of the controller chips in VGA cards. The thing about the CRTC chip is it's really just a programmable counter, and the actual video generation must be handled external to the chip. That's why for example, I could modify the PET to do colour video.
Steve


      From: Mia Magnusson <mia@plea.se>
 To: cbm-hackers@musoftware.de 
 Sent: Saturday, March 24, 2018 5:54 PM
 Subject: Re: PET Graphic, Font, 40/80, Composite and Audio Boards
   
Den Sat, 24 Mar 2018 00:21:39 +0000 (UTC) skrev Steve Gray
<sjgray@rogers.com>:
> No, the 8296 (and D) use exactly the same character rom. The 4000 and
> 8000 series machines can also do this 10-pixel tall character height
> thing. On all these PETs there is a little circuit that ensures that
> only the first 8 pixels are displayed and that the 2 extra lines (or
> more) are blank. Steve

Oh, so does this mean that the monitor is a multi sync (15 and 18 kHz),
or is the 350 line information about the B series monitor incorrect?

Or is it rather that (especially US versions) the low profile with
external monitor versions of the B series uses fixed frequencies for
both vertical and horisontal, and thus can't have more than 8 scan
lines per character row, but the high profile buildt in monitor
versions can use 50Hz even in "NTSC land"?

>      From: Mia Magnusson <mia@plea.se>
>  To: cbm-hackers@musoftware.de 
>  Sent: Friday, March 23, 2018 8:16 PM
>  Subject: Re: PET Graphic, Font, 40/80, Composite and Audio Boards
>    
> Den Fri, 23 Mar 2018 07:26:04 -0700 (MST) skrev vossi
> <vossi@ceffy.de>:
> > I just checked my monitors. Before this I noticed only the light and
> > dark green tubes!
> > 
> > You are right - the 8296D and the 7xx have the same monitor pcb (and
> > the darkgreen tube).
> > The 8096sk and the 8032sk have a different pcb and the light green
> > tube. It's possible that the older monitor is not capable to display
> > the 350 lines
> > - I never tried it.
> > 
> > PS: with the hsg board installed I had to tune the picture-height in
> > the sk to see the whole screen. On the 1702 external connected I
> > have exactly a full screen pic with the hsg.
> 
> My 8296 (not D) uses 8 pixels high characters for upper case /
> "graphics character" mode, and switches to insert some blank lines
> between each character in lower case mode.
> 
> With 2 blank lines between each character row which itself is 8 video
> lines, you get 25 rows of 10 video lines each, minus that you don't
> need to show the two blank lines outside visible text, giving 248
> lines displayed on screen. With rather large borders it might be
> possible to display 350 lines in that mode.
> 
> P.S. this must mean that 8296 has another ROM than the 8096 and 8032,
> right?
> 
> I were so sure that all PETs used 15kHz monitors, and not the 18kHz
> MDA/Hercules monitors. But my 8296 is suspiciously silent compared to
> most 15kHz monitors, even smaller black and white, which usually
> screams really annoyning at 15kHz.
> 



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Received on 2018-03-25 01:00:03

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