Rom hex file help

[stefano]

Hello !
I think you can get the rom yourself via the debug procedure I described. It is much easier than it looks.
Use the ROM version you prefer, patch it and test it on EightyOne first.
It is the only possible shot I'm able to suggest (at the moment), and I think it is worth to try.

[PokeMon]

As far as I'm aware the 60htz treeforth ROM is a rip off of the original PAL and has nothing to do with David Husband of Skywave software ( I will stand corrected if anybody knows otherwise without guessing) so anything to do with a multitasking "clock" is based solely on the 50htz PAL ROM (a paragraph from section 15-0 of the manual refers to 50htz timings only ) and it's inaccuracy is down the differing speeds of the oscillators fitted to each 81.
Some run fast (mine) some run slow.

10 minutes in 2 hours is too much, this is about 8% !
The 6.5 MHz filter has a tolerance of usually +/-1%.
There is a timing error difference as well for the PAL version as well which is about 0.7% plus.

Assuming 6.5 MHz, 1 clock cylce is 153.85 ns, the horizontal frequency is 207*2*153.85 ns = 63.69 us (instead of 64us as TV standard) and the vertical resolution is wrong as 312 lines are generated instead of 312.5. So 1 second of ZX81 is in reality 993.5 ms whioch is about 0.65% too fast. Normally the crystals get slower when aging so this effect may compensate a slow crystal or filter after 30 years.

I guess that the clock is wrong implemented and will miss some counted frames to get that slow.

[stefano]

I'm so curious now.. Pokemon, do you think that the patched ROM will work for you ?

[PokeMon]

I will give it a try at the weekend, when I have more time to test.

[Moggy]

Only just realised as well that due to the screen being too far to the right that when using the editor screen anything that is in the rightmost column cannot be edited/deleted meaning the whole statement has to be wiped out and retyped correctly thus rendering the editor fairly useless.

This manifests itself on eighty one also.

Tried the "realtime" clock routine on a different zeddy and it gained two minutes in three hours no doubt someone will have a clever answer as to why.

I'm still convinced that Mike Wynne made some alteration to the original Skywave ROM to enable it to run in eighty one, if only someone had the original ROM.

[stefano]

have you tried my patch ?

[stefano]

Moggy, I understand that having such a strange result is a good argument... why should the editor be so buggy ??


On the other side it is strange that the same site showing the even the CHIP picture has only the bad ROM images (moving one step backwards).
http://k1.spdns.de/Vintage/Sinclair/80/ ... rth%20Rom/


Do you get the same error with my patch ?

[Moggy]

Hi Stefano.

I will try your patch tonight and let you know result though it will be a long night as I'm not very good at these things.

As for the picture of the Skywave ROM I'm convinced that's all it is a picture and that the ROM image on that site is the H4th image used in eighty one and if it were possible to compare the Skywave ROM image to the H4th image there would be a difference.
Why refer to it as H4th/Treeforth and not Skywave or ZX81 forth? I doubt it is for copyright reasons as there are other ROMS such as Jupiter Ace and Azmic used in eighty one with no copyright worries.
I'm still convinced there are some differences between the Skywave ROM and the H4th ROM used in various emulators but without the original Skywave image we can only guess.

EDIT

Don't know if this is relevant but discovered it on the eighty one changes/update page

Version 0.31 11/11/04
Tidied up the Tape Manager (it's now resizable!). Fixed a bug in the interupt generation code.
This solves a problem where the display would get shifted left or right depending on the code
used to create it. H-Forth and TreeForth ROMs now work correctly (They need to be configured
in a certain way - ROM patches off, 16k of RAM and Shadow RAM on).

[Moggy]

Hi stefano.

In all my confusion I forgot to ask what program are you using to create this "patch"?
Bare in mind I am probably the most stupid on this forum and I am not used to modern assemblers compilers etc.

[stefano]

Almost all the Microsoft DOS and Windows operating system versions include the old "debug.exe" program.
My instructions are based on it.