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When working with the Focal cartridge inserted on my BK 0010, the area displayed on the monitor suddenly reduces to just four lines , instead of the usual 20

Each time this has happened when I've been using a program which uses the X FV() function, to plot lines on the screen, though maybe it has also happened by me clumsily pressing a key combination in the area of the big red STOP key.

It seems rather "deliberate" due to the neat line at the bottom, and the fact I can still list programs within this 36x4 box. But I am no longer to address areas of the screen outside the box.

Does anyone know what the cause of this might be? Is it hardware (the monitor is generally a bit shaky and sometimes fails to show anything but a white horizontal line in the middle of the screen), or is it due to some screen addressing error (though in general the Focal interpreter does not seem to complain when you try to draw a line which goes off the screen), or is it some arcane key combination I accidentally pressed?

I'm using an Elektronika BK 0010-10 with the Blok MSTD 3.069.007 Focal Cartridge, and a black-and-white MS 6105.1 monitor.

  • This reminds me a bit of the Apple ][ hi-res graphics mode where most of the screen would be used for bitmapped graphics but four lines were left (at the bottom) for text. Example here: <en.wikipedia.org/wiki/…>. Any chance the BK0011 had a similar mode you are triggering somehow? – natevw Dec 18 '19 at 17:19
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After pressing "AP2+CБP" key combination computer switches to extended memory mode, in which screen is reduced to 1/4 of original size giving about 12Kb memory of screen RAM to user (extending user RAM from 16K to 28K).

  • I had just got there myself via the Focal HELP (which says "НР СБР" for some reason), but then cross-referencing it with the BASIC manual I found the combination АР2 + СБР, and it toggles modes as you describe. – harlandski Dec 18 '19 at 18:11
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From this page - It is in a section focused on BK0011, but symptoms are very similar:

It really had 32KB RAM onboard but by pressing the 'Expanded memory' button you could send it to the mode when only 4 lines of text were displayed on a screen, and saved video RAM was added to available memory.

I guess it could have the same reason (memory allocation for another usage).

  • 1
    Second this. That was indeed the trick to grab a bit more ram for the user program. Unfortunately, it was of little use if you're programming something that requires the full graphics (a game). – tum_ Dec 18 '19 at 18:01

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