From: Chris_F_Chiesa@cup.portal.com
Newsgroups: comp.graphics,sci.electronics,rec.video
Subject: Need TMS34020 video timing info
Date: Mon, 31 Aug 92 07:04:13 PDT
Organization: The Portal System (TM)


Greetings, Netland!

  I'm working with a graphical display system that uses a Texas Instruments 
TMS34020 graphics display controller chip to generate video signals for a 
multisync monitor.  I'm trying to understand the video waveform control 
registers, in order to create a procedure (or software) for "tuning" the 
video timing to match a particular monitor's optimum scan frequency/ies.
I need to start from the display controller circuitry's master "pixel
clock," a monitor's inbuilt sweep frequency/ies, and a desired "frame
refresh rate," and calculate/deduce a set of values to store in the
TMS34020's horizontal and vertical timing control registers.  Currently I'm
"eyeballing" it and tweaking the registers by trial and error; given a
fixed set of vertical timing values I can get reasonable-looking horizontal
timings, but I still get a lot of "flicker" because the vertical timing
doesn't always agree with what my monitor wants.  (If this description 
doesn't make sense, that just goes to show you how little I currently 
understand video signals and the TMS34020!)

  I have some very minimal documentation that tells me which TMS34020 regi-
sters control which aspects (front porch, back porch, sync start/end, etc.)
of the vertical waveform, but DOESN'T tell me precisely HOW the registers 
affect the waveform.  There's no discussion of what "master frequency" 
drives the waveform, of what "units" (uSec? e.g.) the register values 
represent, nor of how the several registers interact to produce a 
particular desired timing pattern.

  I would very much like to receive information, or pointers to 
information, about the specifics of vertical video waveform generation by 
the TMS34020 chip, addressing the issues raised above, plus any 
relationship the vertical timing may have to the similar HORIZONTAL timing. 
I believe I should start with a "desired refresh rate," monitor's sweep
frequency/ies, and TMS34020's "master pixel clock," compute vertical timing 
parameters (tell me how!), and use the computed vertical timing parameters
to then compute appropriate horizontal timing parameters.  If this is the
right sequence of operations, please confirm and tell me how to do the 
vertical timing calculations (I think I can do the subsequent horizontal
calculations, but feel free to review this for me).  If this ISN'T the 
right procedure, please tell me what IS.

  I'd like to receive e-mail, or even a telephone call, in addition to 
any posting you may follow up with HERE, as I've scattershot this to a 
number of newsgroups including some that I don't ordinarily read.  I 
apologize to those who are offended by this practice (I know some of you
are), but if YOU ever show up with a one-shot question in any of the groups
_I_ frequent, I'll be sure to do YOU the courtesy of a reply just as I
would to a "regular."  Thanks in advance!

   Chris Chiesa
     Chris_F_Chiesa@cup.portal.com

      (716) 724-2029  (Rochester, NY, USA; Eastern time zone; 8A-5P)
      (716) 482-9573  (outside 8A-5P working hours)