AGA + VGA = slow serial

[mwoof]

Hi all,

I have a 1200 AGA 040/25+PPC/160, 1084 and SVGA monitors and 56K modem.  I wish to get rid of the 1084, but when I use a VGA screenmode the modem slows down!  I had read about this problem in the past, but is there a way to overcome it without changing hardware?  (Note: I already have an AmigaOne but wait for OS4 to come out, as I can not justify Linux messing the files just because it crashed and I had to press the reset switch...  :-?)

Thanks.

[KennyR]

It's a problem with custom chip bandwith. VGA modes totally saturate AGA bandwidth, and Amiga serial has no buffer. The solution would either be not to use VGA, or not to use the on-board serial. The 2nd solution would mean adding extra hardware.

[Karlos]

Kennys right. running VGA modes on the AGA chipset sucks up most of the bandwidth.

If you wish to use both reliably, your options are:

1) A scandoubler/flickerfixer. This will allow you to show 15kHz modes on a VGA monitor, freeing up bandwidth for the serial port (and everything else on the custom chip bus).

2) A graphics card. Depending on your needs/cash you can go for a blizzardvision or either a mediator or grexx (if you can find them). The latter allow various PCI devices to be used, including IO cards (I think).
A graphics card, even the BVision, makes a huge difference to general use but old custom chip banging hardware wont be able to use it.
Whichever you choose, a tower case is needed.

3) A buffered serial port expansion of some kind.

[bloodline]

Karlos wrote:
Kennys right. running VGA modes on the AGA chipset sucks up most of the bandwidth.

If you wish to use both reliably, your options are:

1) A scandoubler/flickerfixer. This will allow you to show 15kHz modes on a VGA monitor, freeing up bandwidth for the serial port (and everything else on the custom chip bus).

2) A graphics card. Depending on your needs/cash you can go for a blizzardvision or either a mediator or grexx (if you can find them). The latter allow various PCI devices to be used, including IO cards (I think).
A graphics card, even the BVision, makes a huge difference to general use but old custom chip banging hardware wont be able to use it.
Whichever you choose, a tower case is needed.

3) A buffered serial port expansion of some kind.

Since the AGA serial port is fine for most uses, like a modem. I think that Option 2 is the most sensible.

A GFX card will brighten your life in more ways than one.

[Ryu]

you can pick up a used Bvision for about £50 if you look around.

I do have one suggestion... if your using OS3.9 with Boingbag2 you could try using an older version of serial.device or use the internal device driver if your using miami as your tcp/ip stack. IIRC the BB2 serial.device is buggy...

[MASACREWILL]

..sorry for an offtopic, but I would like to ask where can I get a scheme of RGB to VGA adaptor. I have tried to search the Aminet, but there were only some old schemes with additional circuits, and I want just a simple one. Thanx for your help.. ;-)

[darkcoder]

I add another option:

4) use VGA 640*480 with 16 colors or 320*480 with 256 colors, you use more or less the same bandwidth as PAL 640*256 with 256 colors (I know it's not nice to be so limited in resolution or color, but this really requires no extra hardware! :-)

[Jose]

The cheapest and more efficient solution would be buying a buffered serial port that connects to the clockport. The PortJnr for example does the protocols in hardware.  It's not that cheap for what it is (just a serial port) but it's very cheap compared to other solutions. If you're persistent you can't find some in the second hand market.
A BVision Gfx card would make a big difference to your system though and you can get them like already said for around 50£. Although this would apparently require towering and so more money I've hear people haing it in A1200 desktop cases.... beware of temperature problems , be sure to have the necessary cooling..

[CaptainHIT]

@MASACREWILL:

Try this url for a basic scheme:

http://www.home4u.de/martintauchmann/a-vga.html

You only need one capacitor and two resistors, that's all :-D

[mwoof]

darkcoder wrote:
I add another option:

use VGA 640*480 with 16 colors or 320*480 with 256 colors...

I had this idea too!   :-D  I run a utility which opens additional screens and used 640x480 in 16 and then 32 colours.  I also had to make the modem slower (38400 instead of 57600), but since I use it mainly for chats these days it won't be too much of a bother.

Thanks everyone for the advice.  :-)  In the meanwhine, I had another thought: is is possible to make an Amiga to composite cable, and if so would it have a better picure than the built-in composite output?  I have one of those TV tuner devices for VGA monitors and the Amiga->Scart does not give a picture through the VCR...  :-(