english greek
Home arrow Forum

The Newbrain Forum

Anything about the Newbrain Home Computer

You are not logged in.

  • Index
  •  » Service
  •  » NewBrain repeating first Screen row over and over...

Add to: Mr. Wong Add to: Webnews Add to: Icio Add to: Oneview Add to: Folkd Add to: Yigg Add to: Linkarena Add to: Digg Add to: Del.icio.us Add to: Reddit Add to: Simpy Add to: StumbleUpon Add to: Slashdot Add to: Netscape Add to: Furl Add to: Yahoo Add to: Spurl Add to: Google Add to: Blinklist Add to: Blogmarks Add to: Diigo Add to: Technorati Add to: Newsvine Add to: Blinkbits Add to: Ma.Gnolia Add to: Smarking Add to: Netvouz Information

#1 23-03-2016 18:44:21

scouter3d
Veteran

(Hover for details)
Registered: 10-08-2011
Posts: 33
Reputation :   

NewBrain repeating first Screen row over and over...

Hi,

I have here an AD, which is booting fine, the VFD Display works fine also...

...but: on the videoscreen only the topmost row of characters is displayed (all the other 24 rows are exact copies of row 1)

looking at the schematic i am overwhelmed by all the signals used for screengeneration any clue, where the rows are counted?

any input or guide, how the screenimage is generated is welcome...

TOM:0)

 

#2 24-03-2016 18:11:40

cdesp
Moderator

(Hover for details)
Location:  : Kilkis, Macedonia, Greece
Registered: 27-07-2008
Posts: 82
Reputation :   

Re: NewBrain repeating first Screen row over and over...

Hi Tom,

Look at the schematics named 1 (mainboard).
Ics 447 and 468 are counters 74393.
On schematics named 2 (mainboard) ICs 422 and 423 are also counters.

At the start of each frame NB outs a 8bit value which holds the bits after bit6 for the NBstart address (A7,A8,...)
if Bit 6 must be set the NB makes another out to set it.
ICs 422 and 423 are set by this out (8bit) so these are the address counters that select the RAM address to be read (DATA lines) either by IC 453 (Char eprom this shoould be your case since you are on line 1) or IC454 (graphics out).

That was just to get an idea on how the screen is produced. So since all these have almost nothing todo with the column or row counting on screen i must say that your problem should be on ICs 447 and 468 which produce the syncing signals CSYNC and a lot of other sigs that have to do with the screen.

IC 458 counts the 8 or 10 lines to display the char on text screen.
Ram goes from Addr 642 to 642 + 40 chars to read the 1st line of the char matrix then 458 increases and ram goes again from Addr 642 to 682 to display the second line
until IC458 reaches 8 or 10 lines in which case address increases to 642+64(=40chars +24 excess chars)
and the whole thing starts again.

Hope this helps.

Chris

 

#3 28-03-2016 21:06:15

scouter3d
Veteran

(Hover for details)
Registered: 10-08-2011
Posts: 33
Reputation :   

Re: NewBrain repeating first Screen row over and over...

Thank you Chris!

Your explanations of the NewBrain video circuit helped a lot!

I changed a few chips you recommended, but the fault still remained, then i remembered you mentioning, that after each Character row (8 or 10 lines) the NewBrain adds 64 to the address and there is a signal labled 64A in the schematic! After replacing chip 444 and 445 the NewBrain works again!!!!

Thanks again for pointing me in the right direction and helping me understand the Newby a bit more...

TOM:0)

 
  • Index
  •  » Service
  •  » NewBrain repeating first Screen row over and over...


Add to: Mr. Wong Add to: Webnews Add to: Icio Add to: Oneview Add to: Folkd Add to: Yigg Add to: Linkarena Add to: Digg Add to: Del.icio.us Add to: Reddit Add to: Simpy Add to: StumbleUpon Add to: Slashdot Add to: Netscape Add to: Furl Add to: Yahoo Add to: Spurl Add to: Google Add to: Blinklist Add to: Blogmarks Add to: Diigo Add to: Technorati Add to: Newsvine Add to: Blinkbits Add to: Ma.Gnolia Add to: Smarking Add to: Netvouz Information

Forum Tools

Board information

Board statistics
Total number of registered users: 113
Total number of topics: 92
Total number of polls: 0
Total number of posts: 345
User information
Newest registered user: gillespienewbrain
Registered users online: 4
Guests online: 4157

Powered by Agora 1.0.4 Acropolis

© Copyright 2007 - 2008 Joomla Me!. All rights reserved.

Powered by Elxis - Open Source CMS.
Copyright (C) 2006-2018 Elxis.org. All rights reserved.