i think is the screen active bit. When i start the map-demo i begin to copy all to the VDP, like Kurt. But i don`t set screen OFF, so maybe i lose some pixel. And then after every reset, the software start again and do the copy again. But now the TMS has more to do because the demo is running, and s...

thank you for the test.
then we must check 2 points:

1 what exact do the CV at the startup?
2 what to the CV when we press reset?

we don`t handle, i do not, the reset button.

I use the same sort of programming on other hardware with TMS, and all is fine on real hardware.

yes i am right, i check Kurt`s source, he init the VDP with Screen OFF. After he is finish with copy he do: LDA #$E2 ;new value including set screen active bit STA VDP_Status_Write LDA #$81 ;write into register 1 STA VDP_Status_Write ;see comments on that BIOS routine above and set the bit to active...

As i remember Kurt set the screen active bit OFF then write all to the VDP RAM, and when all is finish turn on the screen.
I really think you only have this timing problem outside the VBL.

but in the VBL when the TMS has nothing to display, you can write as fast as possible. After an address is written, the VDP needs 2uS to retrieve the data. Between reads, the VDP needs 8uS to get the next piece of data. And now, the variable part - the VDP only provides a CPU access window from ever...

speed of copy to vdp can be the source for the error, this can be with my software also because i don't test on real hardware on the moment. The way the VDP works is a sort of a "best effort" approach. When you write data to the data port, the VDP will copy that data to VRAM when it's ready to, and ...

yes, in the map-demo and in the game i write now i access the register or move to VDP memory only in the VBL. I also use then the VBL for set timing flags for the main loop. My source code part for the VBL is strange and long because i use unrolled loops etc., but then i enough time to do all the VD...

Hi Carlsson,

most TI99/4a and Memotech programmer i know never touch the VDP in a scan-line.
When is absolute needed then disable before the interrupt and turn on after again.

Some emu`s fix VDP trouble`s like for example the 8-sprite error in Half-Bitmap-Mode, but real hardware not.

Hi Carlsson,
i like your Work. Great Game.

Yes we Need this like the multicard for the colecovision.
I speak with atarimax about that, wait for answer.

Before i think about to buy an eprom Simulator, but is very Big and
expensive.