[Coco] I2C - Is it possible?

[gene heskett]

On Saturday, July 23, 2011 11:11:42 AM James Dessart did opine:

> On Sat, Jul 23, 2011 at 4:42 AM, Nick Marentes <nickma at optusnet.com.au> 
wrote:
> > Just wondering if anyone has any idea if it's possible to 'bitbang' an
> > I2C interface on the CoCo?
> > 
> > There so many tiny I2C circuits available (including VGA) that I was
> > wondering if there was any way to bring some of these devices to the
> > CoCo?
> 
> Wikipedia has this to say:
> http://en.wikipedia.org/wiki/I�C#Example_of_bit-banging_the_I2C_Master_p
> rotocol

From what I get from this article, the coco's bit banger port is not 
capable since both lines need to be both bidirectional and open collector 
for output.  I would think a suitable chip could be cobbled up and made to 
work under nitros9, possibly even somewhat along the lines of The Forgotten 
Chip idea but with a separated jack.  I built that, and used it in a coco2 
for about 14 years in my EDISK kit for the tv station.  Zero problems with 
it.

We had one device there at WDTV that used I2C.  When they said that 
protocol was distance limited to 39 feet, they meant it.  The control head 
for an effects device needed to be beside the switcher's panel so that the 
CG operator immediately to the TD's right could reach it.  The unit also 
needed to be within a 2 foot range of the switchers main rack for color 
phasing matching.  This resulted in a trench run of about 42 feet.  Could 
not be made to work.  I finally ran the control cable straight up into the 
suspended ceiling and ran it across the tiles to a point above the control 
position & dropped down to it, which allowed me to cut about 3.5 feet off 
the cable.  At 38.5 feet, it worked flawlessly.  But that experience pretty 
well dynamited any chances of us buying any more gear that used I2C for a 
control interface.

Cheers, gene
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
We come to bury DOS, not to praise it.
(Paul Vojta, vojta at math.berkeley.edu, paraphrasing a quote of Shakespeare)