[Coco] [coco3] upscan video converter

[RJRTTY at aol.com]

In a message dated 7/16/05 3:44:42 PM Eastern Daylight Time, 
jdaggett at gate.net writes:

<< 
 1) The block diagram seems a bit unclear. It looks as if all the COCO 3 RGB 
signals 
 go to the ISC523 and that appears unlikely.  >>

    I didn't mean to imply the ICS1523 used all the signals on the coco3 RGB
video output.    I was just trying to keep the diagram simple.   It does use
the horizontal sync and line locks to it generating  1X  and  2X   clock
frequencies which are passed on to the AL875 and AL250.   Sorry
for the confusion.

<<
2) I am a bit confused on the outputs comparator and signal translation box. 
I 
believe that you are doing some form a level translation of the COCO signals 
to that 
needed by the Averlogic AL875 part. Is there some I2C control lof this 
circuit? 
>>

     Again I left a lot out to keep it simple.    The comparator and a few 
support
components translate the PIA line (pin #10) and vertical sync ( pin# 9)
of the coco3 RGB video out signals into the data and clock signals
respectively of the I2C bus on the board.   It's not controlled by the I2C
bus but GENERATES the I2C bus.   The comparator basically does
level translation.

<<
3) the ICS523 part supplies the video clock as well as the 2x clock required 
by the 
AL875. Was this part chosen because of its versitility? Does it offer a space 
savings 
in board lay out over a discrete crystal and divder logic? 
>>

       This is not my first attempt at this circuit.    In the first run, I 
designed
the converter with a PLL circuit using discrete components using a 74LS04
based oscilator , a 74LS74 flip flop, a 4046 phase comparator  and a varactor
which I dont have the number to just now.     When complete the circuit
using the discrete components took more board space and cost more than the
24-pin SOIC package of the ICS1523.    I am using those first boards
to build beta test units and to prototype the final design using  the
ICS1523 and ATtiny12 microcontroller before I actually order new
boards.    Live and learn.

<<         
I understand the need for the microcontroller to interface to the I2C bus. I 
remember 
from the previos thread that trrying to control I2C via the COCO is a bit 
difficult. I 
still wonder if there is some provision for In Circuit Programing of the 
Atmel part? It 
does appear to be that this is just not a upscan converter but able to 
utilize the 
Averlogic parts more of their capabilities. 
>>

      As a matter of fact the coco3 controls the I2C bus quiet easily and
dependably.    The major reason for the microcontroller was so that
the user didn't have to power up without a display.     Since I had to
include it I decided to take full advantage of its capability.  The coco3
can ignore the microcontroller completely.   Even if it is damaged or
nonfunctiional the converter could still be used if there wasn't any
other problems.

       You are correct.    I have already written software that allows
the user to control the contents of all the Read/Write registers of the
two Averlogic and ICS chips.  Some options include border colors or
overlay messages and size or position of the screen borders.  Even
configuration to meet other custom video standards like PAL.
There are many possiblities for anybody who wants to experiment
with them and simplicity for those who dont.

    Thanks for your questions.   They help to get the details out to
everybody.

Roy