Re: [uCsimm] Dragonball on TV

From: Tom Walsh (
Date: Sat Jan 06 2001 - 08:17:06 EST

> Raj Kumar wrote:
> Hi everybody,
> I am working on a project that requires me to interface a MC68EZ328 to
> a standard colour TV. I am planning to use uClinux.
> Has anyone out there worked with / interfaced a low cost TV/Video
> controller to the Dragonball ? The primary objective is to display
> text (English) onscreen. Bit mapped graphics would be great ! Colour
> display would be even better !!
> I need to keep costs low. I am looking for a simple / single chip
> solution (without extra Video memory etc.)
> Has anybody tried/thought of tweaking the onboard LCD controller to
> generate TV timings ? (HSync/Line Pulse of 15 KHz and VSync/Frame
> Pulse of 50 Hz) ?

Interesting idea, probably could be done as the lcd screens do function
much the same way as a crt, both require "bit pumps" to keep them
refresehed. The internal LCD controller would only give you a Black &
White picture, the controller is not fast enough to generate much
color. However, the TV screen is interlaced to reduce flickering and to
"bulk up" the viewing image, it is actually the same image shown a
second time (interlaced) but shifted slightly on the screen to "fill in
the blanks" in the first image. The TV raster beam does not behave
exactly like like the non-interlaced beam of the computer CRT.

The information content in a TV picture is a lot lower than you would
expect, remember the Apple II, Commodore 64, and other, computers that
used a TV set as the primary monitor? There is a reason that there was
only 40 characters on the screen, bandwidth. As long as you are aware
of the limitation.

As far as "low cost" COLOR is concerned, I don't know how well you can
achieve that. Many of the video chipsets that were used in the early
home computers to drive the RF modulators / monitors have disappeared
from the market. You may be able to put together a Programmable Macro
Cell to do the job, some of the Macro Cells have reached densities into
which you can model microprocessors. You would have to use high speed
SRAM as a dual-ported RAM, as you could take some pins on the Macro Cell
and make them appear to the Dragonball as a small RAM.

I think that you are attempting to make a silk purse out of the
DragonBall. IMHO, you would be better off using one of the System On a
Chip ARM processors. For example, Cirrus Logic has some ARM 7500 & 7212
chips that have more powerful LCD controllers built in. Also, the ARM
family is capable of much higher performance, MIPS, than is achievable
from the 68K family (recall the announcement by Motorola of thier
intention to begin incorporating ARM cores into some of thier

On a lower end of performance, and cost, as you may be using the uCsimm
as an already designed board, look at the Atmel EB-01. The Atmel EB-01
is a pre-made board, not too expensive, uses the ARM7TDMI chipset, more
powerful than the DragonBall, and already has a port of uClinux running
on it (see: '').



Tom Walsh - WN3L - Embedded Systems Consultant
'', ''
"Windows? No thanks, I have work to do..."
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