Cannot use 32K graphics modes?

Hardware questions and modifications

Cannot use 32K graphics modes?

Postby beckman » Fri Jun 28, 2013 9:03 am


I have just got a PCjr, and most of it is working just fine. However I cannot get it to go into 32K graphics modes.

It is a 128K model (128K shows up on boot screen). In cartridge basic, "SCREEN 0" though "SCREEN 4" work fine. As does "WIDTH 80". But "SCREEN 5" or "SCREEN 6" give "Illegal function call".

From assembler (in DOS 3.10 DEBUG), getting into 320x200 16-color mode with:

mov ax,0009h
int 10h

gets me a screen of garbage and a hung system.

This seems odd. Any suggestions?
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Re: Cannot use 32K graphics modes?

Postby jmetal88 » Fri Jun 28, 2013 10:26 am

I think 16k is all that's enabled by default. To do 32k I had to set an option for it in JrConfig.
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Re: Cannot use 32K graphics modes?

Postby Brutman » Fri Jun 28, 2013 4:02 pm

I think that in Cartridge BASIC you have to issue a "CLEAR ,,,32768" first. That should be in the BASIC reference manual. That sets the video buffer up for the extended screen resolutions.

The BIOS call should be working - I can't explain that, except that perhaps you are responsible for wiping out the memory before making the call.

And also, you are probably not using JRCONFIG or any other memory manager on a 128K machine. But if you are they need to be told to reserve 32KB of space for the video buffer.

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