Sinclair ZX80 / ZX81 / Z88 Forums

just for fun try running this little program on whatever hardware or software you use and see if you get this...



on real zeddy you do not get the character corruption, but instead the whole display moves up by 1 line.

eightyone does not handle it properly. and vb81 crashes, haven't tried anything else.

Andy

Got this on EO:
Siggi

Hi Siggi,

That looks the same as what i get on EO (but i have border set to none) so don't see the very top line, i was more interested to see the results of other hardware or emulators other than EO, e.g homebrew systems.

on a real ZX81 the characters remain intact, but the whole screen moves up by one scanline.

Regards Andy

That appears on my ZX81 laptop (a ZX81 board with LCD display via AV output):
Siggi

Yes i expect a genuine ZX81 to work correctly, did you notice a vertical shift of 1 scanline ?

Andy

Yes. After I added a small delay (at line 45) I noticed, that the screen jumped upwards a little bit ...

Siggi

odd isn't it ? i have a theory as to why it does it, and why EO does what it does.

but now i wait for some homebrew result

Adny

Works ok no crash on My version of Vb81 V 1.30.3 update 27/7/11

I'm intrigued.

Works ok no crash on My version of Vb81 V 1.30.3 update 27/7/11

Hi,

Vb81 XuR is out !

The main VB81 specificity is to ignore the Rom display routine...

It just mirror the screen buffer (D_file), and call back it on the screen.

In VB, displaying the "true" scanned line screen, will push down the computer display to a critical speed.
All of HRG routines (using asm opp-codes, like IY in psedo-HRG) are redirects in specified routines (like HRG cards).
The XuR can't run properly if your choose to use an home made routine.
Almost if you had to force the XuR to execute a part of Rom display code.

The Xur just get the D_file, perform a AND on to byte to display... and show you the ZX81 screen.
NoCash81 won't work too.

I Had to code several routine to display psedo-HRG...
But, the main vb routine can't add a delay in screen display, using 4bytes asm opp-codes command.
(the Xtricator code don't run on the XuR.)

I pointed this leek in my latest "Star Trek" game ...
It Worked on the Xur, but destroyed the D_file on EO.
I obviously printed an illegal character on the screen !

Just try to poke a $F8 - 248 byte in the D_File.
The screen won't be destroyed on the XuR.
But, on EO, the screen will be affect to this byte (aspecily due to the display control bit).

Hack the the display routine, using the XuR, can't affect the emulator display.
You can code and trace an HRG routine, but nothing will be displayed if the XuR HRG is not intercepted/swished on!

The test ran and loop in the Rom, but the process don't affect your screen and slow down (Hang?) the code!
We had to try on sZ81 !