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ZX Spectrum extra graphics modes

32×192 cells

The main extra screen mode has 32×192 attribbutes cells 8×1 pixels each. (The standard screen has 32×24 attribbutes cells 8×8 pixels each.) A screen in this mode takes 12kB RAM. This mode can be used on Timex (OUT 255,2), Sam (MODE 2) and some Russian clones. Such screens can be displayed also on MSX in SCREEN 2 mode.

It looks possible to upgrade a standard ZX Spectrum to display this mode. The Z80DMA chip in MB-02 interface can be used to simulate this mode (this is called multitech). It is possible to display images in this mode on every ZX Spectrum, but this is software trick and consumes most of CPU time (this is called multicolor). However, there's not much software support for this mode.

512×192 mono

Second main extra mode is monochrome, but 512×192 pixels. It also takes 12kB RAM. Only Timex computers can display it. This mode was mainly used to display 64 or 80 columns text screen. There are at least two graphis editors for this mode, working on Timex. Beside, there are BASIC64 and some CP/M implementations.

512×192, 4 colors
256×192, 16 colors

The Sam Coupé introduces next two extra screen modes, each takes 24kB RAM. Third is 512×192 pixels, each pixel in one of 4 colors from palette of 128 colors. Fourth is 256×192 pixels, each pixel in one of 16 colors from the same palette. These modes are supported by graphics editors for Sam. The 4/16 colors can be different in each screen line thanks to interrupts generated changed after the line is displayed.

The MSX 2 can display such pictures in SCREEN 6 and SCREEN 5 modes, respectively.

256×192, 256 colors

The SPEC256 emulator has a screen mode 256×192 pixels, where each pixel can be in one of 256 colors. The screen takes 48kB of memory. Animations can be done in real time, as the screen is controlled by eight Z80CPUs working parallelly, so each of them has only 6kB of screen to drive, as in original ZX Spectrum.

Switched modes

Since Timex and ZX Spectrum 128K have two areas from which the screen can be displayed, there's a possibility to switch the areas at every frame interrupt (50Hz). This gives an impression of more colors on screen. The colors looks darker, old TV set is recomended. This is sometimes called interlace, but this isn't a true interlace, as in TV broadcasting. TV displays odd then even half-frames in 40ms, while computer displays only odd half-frames in 20ms.

More?

Some other modes are used on Russian clones. If you know something about them, please add a note.


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Files for download

techdraw.zip 11.3kB (2005-09-15 20:23)
Tech Draw for Timex. 512×192 mono mode (Timex).
color_d.zip 20.7kB (2005-05-22 14:36)
Color Draw for ZX Spectrum. 32×192 color cells (Timex, Sam, MSX, multitech with MB02).

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© 2009-12-28 21:50 Jarek Adamski, http://8bit.yarek.pl