Duo VRAM

[techknight]

Do they make a 524,288 by 8 bit VRAM IC?

just rumbling around in my head about the potential of beefing up the internal VRAM for the Duo. It has 2 onboard VRAM ICs, and they are 262,144 by 8bit dual-port DRAM/SAM VRAM ICs.

 

[unity]

Google found this:

262,144-Word x 16-Bit or 524,288-Word x 8-Bit

http://www.alldatasheet.com/datasheet-pdf/pdf/11095/OKI/MSM27C452CZ.html

 

[techknight]

thats a ROM.

not a VRAM. Ive already googletubed my eyes out, thats why im asking here ;-)

 

[unity]

Well I try. It was under the VRAM category though!

 

[techknight]

Yea, that was odd.

 

[Trash80toHP_Mini]

The info on VRAM in the Duos and other PBs from the era is poorly documented.

I'm not certain that upping the VRAM is going to help in and of itself. I suspect the RAMDAC in(?) the CSC Video Controller is at its limits doing what it does. The Duos used the GSC controller through the October 1994 of the 250. The 270c introduced with the 250 that month switched to the CSC controller, which remained unchanged through the 2300c/5300xx rollout in Aug of 1996. The 2300c retained CSC while the ECSC was used in the 5300 series and later 1400 series.

I think it was MadDog over on 'fritter who was trying to do increase the VRAM of the 2300c, but I think he was planning on stacking the extra VRAM on top of the standard chips. I do know that he successfully replaced the CSC Video Controller of the 2300c with the ECSC Video Controller from a 1400. That's on my list for the SuperDuo and I'm fairly sure doing so is a given for making use of additional VRAM in the 2300c.

Dunno for sure though, that was a long time ago.

 

[techknight]

Only reason why I asked, is that way I can get the 16bit color for the 640x480 instead of having to reduce back to 640x400, because that looks like poop.

I do have a dead 1400 board that dropped out and wont power back on anymore, hmmmm..............

 

[Trash80toHP_Mini]

Yep! I contacted you about doing the SMT rework for this hack for the SuperDuo way back when, interesting project . This is a good place to put some notes and collablrate:

VRAM Locations 2The 512KB display buffer on the main logic board consists of 2 VRAM chips. One of the

VRAM chips is located on the front of the main logic board and one is located on the back

of the board.

Note

The number of colors available in 16-bit mode is less than the theoretical

maximum due to the limitations in the color LCD technology. Many

color values exhibit noticeable flicker. The computer’s CLUT omits the

unsatisfactory colors, making about 4,000 available. See the Appendix,

“Color Lookup Table,” for more information.

Flat Panel Display Circuitry 3The flat panel display circuitry in the Macintosh PowerBook 5300 computer emulates a

NuBus video card installed in slot $0. There is no declaration ROM as such; its

functions have been incorporated into the system ROM. The display circuitry includes

the new ECSC controller IC and a display buffer consisting of 1 MB of VRAM. The LCD

display is compatible with software that uses QuickDraw and the Palette Manager. The

display supports color table animation.

Flat Panel Display Circuitry 3The flat panel display circuitry in the PowerBook 1400 computer emulates a NuBus™

video card installed in slot $0. There is no declaration ROM as such; its functions have

been incorporated into the system ROM. The display circuitry includes the new ECSC

controller IC and a display buffer consisting of 1 MB of VRAM. The LCD display is

compatible with software that uses QuickDraw and the Palette Manager. The display

supports color-table animation.

An ECSC (enhanced color support chip) IC provides the data and control interface to the

LCD panel. The ECSC IC contains a 256-entry CLUT, RAMDAC, display buffer

controller . . .

Couldn't find the 2300c DevNote, but I'm guessing the limitations are 512k VRAM and the CLUT/RAMDAC equivalent for an LCD Video Subsystem.

 

[Trash80toHP_Mini]

No wonder I couldn't find it! Google finds it at preterhuman just fine, but when you download it the filename is "PowerBook 160-180.pdf" :

Display Controller ICThe CSC (color support chip) IC provides the data and control interface to the LCD

panel. The CSC IC is also used in the Macintosh PowerBook 500 and 280 series

computers. The CSC IC contains a 256-entry CLUT, RAMDAC, display buffer controller,

and flat panel control circuitry. For more information, see “Displays” on page 14.

___________________________________________________________________________

The color display can operate in either of two modes. In 8-bit mode the display has a

640-by-480-pixel area and can display up to 256 different colors at a time. In 16-bit mode

the display has a 640-by-400-pixel area and can display thousands of colors.

The user can select either color display mode by using the Monitors control panel.

Because the VRAM is a fixed size, 256K by 16 bits, it can handle only a certain amount of

data. When the user selects 16-bit mode, the system software resizes the display area

down to 400 lines instead of 480 and centers the display area on the screen, leaving black

bands of 40 lines each at the top and bottom of the screen.

Note

The number of colors available in 16-bit mode is less than the theoretical

maximum due to the limitations in the color LCD technology. Many

color values exhibit noticeable flicker. The computer’s CLUT omits the

unsatisfactory colors, making about 4000 available. See the appendix,

“Color Lookup Table,” for more information.

There, now I can look this over at work in my downtime tomorrow.

Have you swapped in that ECSC yet, techknight?

 

[techknight]

No not yet, Trying to get the system software straightened out first. It has some crazy virus, or parental control somethin another on it.