Why does H.E.R.O. have a rolling screen on ZEsarUX and EightyOne?

[sharopolis]

So the conversion of the classic HERO for ZX 81 by Nocash runs fine on the NO$ZX emulator from Nocash themselves but if I try to run it on ZEsarUX or EightyOne I get a rolling screen, this GIF is a capture of what I'm seeing.



With EightyOne I can change the vertical hold in the TV emulation to stabilise the picture, but I haven't found any option in ZEsarUX that has any effect.
Does anyone know what this happens? Does this same effect occur on a real ZX81?
No other game I've tried does this, even other WRX hi-res games from Nocash like Beamrider.
Is there any way around it on ZEsarUX too?

[David G]

It's not the ZX81, it's the TV, or in the case of emulators, the emulated TV. Hi-res games alter the video signal timing, and if the timing is far enough off, on a physical TV you have to adjust the vertical hold to compensate

[Exile]

As David says, HERO generates a TV signal that is out of bounds for some TVs. I have to adjust the emulated TV settings in picozx81 to get a stable image.

No other game I've tried does this, even other WRX hi-res games from Nocash like Beamrider.

There are a few programs that generate strange displays. A couple of classic ones are QS Defenda and Nova2005.

http://www.zx81stuff.org.uk/zx81/tape/QSDefenda
and
http://web.archive.org/web/201703091715 ... NOVA2005.p