Software for an S-100 Bus Computer using MSX video hardware.

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By Manuel

Ascended (19270)

Аватар пользователя Manuel

04-02-2014, 21:05

monahanz wrote:

But this will not test V9938 hardware. I'm having a problem getting the software (initilization) to set the hardware (v9938 chip) so it displays correctly.

If you use the register values that MSX BASIC used to set up the mode (which are the ones that PingPong showed) you should be able to get the V9938 in the right mode, right?

By monahanz

Rookie (21)

Аватар пользователя monahanz

08-02-2014, 22:24

flyguille, thanks for the above information. Appreciate the time and effort.

I modified my software to insert the above values in all the above registers.
Unfortunately it did not work, however the screen does look different and seem like it is continuously writing spaces sequentially to the whole screen in some kind of high resolution mode.
I’m wondering if I have the character generator or something else placed wrong.

I have made a link specifically for you at the bottom of this page
http://s100computers.com/My%20System%20Pages/VDP%20Video%20B...

Under "For Leon" there is a "here" link that contains a .zip file with the above source code.
Do you know where specifically the start address of your screen character generator.
Is source for it available.

John

By Eugeny_Brychkov

Paragon (1232)

Аватар пользователя Eugeny_Brychkov

08-02-2014, 22:51

John, let me repeat my question - which issue are you having right now? Can you describe it concisely?

By PingPong

Prophet (4093)

Аватар пользователя PingPong

08-02-2014, 23:12

monahanz wrote:

flyguille, thanks for the above information. Appreciate the time and effort.

I modified my software to insert the above values in all the above registers.
Unfortunately it did not work, however the screen does look different and seem like it is continuously writing spaces

OK, let's assume you've done sw things right.
Maybe a hw problem? the v9938 used some kind of interleaved vram access, and from what i know, there are few msx that employ the v9938 with only 16 kvram. in those configurations, we do not know how physically (electrically) the address lines of the chip are connected to vram. I suspect that the start of mirroring take place at an address with an offset that is a power of 2. maybe i'm wrong but i suspect some kind of hw connection issue

By monahanz

Rookie (21)

Аватар пользователя monahanz

08-02-2014, 23:36

PingPong, the board has four TMS4464's, so 128K of RAM.
Since the V8898 chip is the only connection to this RAM (i.e. the system Z80 does not in any way talk to it) in theory it should not matter how the Address lines are hooked up, refreshing I suppose in theory, but definitely not a screen line display issue. Anyway the 8 address lines AD0-AD7 go directly to all four A0-A7 DRAM chips.

Eugeny_Brychkov, the problem I'm having is that while the board displays 40X24 (Text1 mode) correctly. When I try to go to 80X24 (Text 2 mode) I get duplication of the top text about half way down the screen. If you can go to here:-

http://s100computers.com/My%20System%20Pages/VDP%20Video%20B...

And scroll down to the last picture on the page you will see that the top line of text repeats (exactly) again in the middle of the screen starting towards the right hand side . If I enter text from the keyboard it duplicates at both locations.

By Eugeny_Brychkov

Paragon (1232)

Аватар пользователя Eugeny_Brychkov

08-02-2014, 23:40

Ok, then you have had a solution a week ago. It is NOT software problem. It is problem in your HW design.
http://www.msx.org/ru/node/44196?page=2#comment-230344

By monahanz

Rookie (21)

Аватар пользователя monahanz

09-02-2014, 00:38

Eugeny_Brychkov I just tried switching the pins by bending out pins 55 & 56 of the V9938 and connecting pin 55 to pin 10 of a DRAM chip and pin 56 to pin 6 of the DRAM chip. Get exactly the same screen output -- duplication of the text.

When you think about it the above could should not make a difference because the Z80 never accesses the video RAM and has no way of knowing its layout. The video chip does not really care/know actual RAM locations either so long as each 16 bit address provides a unique location. The only time the actual address arrangement is an issue is for DRAM refresh -- clearly not a problem in this case. If for example, as we have with PC-VGA boards ,the CPU also accesses RAM directly then the exact RAM arrangement becomes important.

John

By Eugeny_Brychkov

Paragon (1232)

Аватар пользователя Eugeny_Brychkov

09-02-2014, 08:30

monahanz wrote:

Eugeny_Brychkov I just tried switching the pins by bending out pins 55 & 56 of the V9938 and connecting pin 55 to pin 10 of a DRAM chip and pin 56 to pin 6 of the DRAM chip. Get exactly the same screen output -- duplication of the text.

Good, so now we know it is not the problem here. I described the proper way connecting DRAM chips, and until you make your desing per specification all further troubleshooting may be useless.

monahanz wrote:

The video chip does not really care/know actual RAM locations either so long as each 16 bit address provides a unique location. The only time the actual address arrangement is an issue is for DRAM refresh -- clearly not a problem in this case.

In this case - you proven it is not (small portion of VRAM is involved). What is about having chat through skype?

By monahanz

Rookie (21)

Аватар пользователя monahanz

09-02-2014, 08:41

Sorry don't use skype.

By monahanz

Rookie (21)

Аватар пользователя monahanz

09-02-2014, 08:42

you can send me an e-mail using monahan (AT) vitasoft.org

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