[Coco] Telepak RS232 Pak

[Roger Taylor]

At 11:49 AM 1/17/2009, you wrote:
>On Saturday 17 January 2009, Roger Taylor wrote:
> >At 03:53 AM 1/17/2009, you wrote:
> >>On Saturday 17 January 2009, Roger Taylor wrote:
> >> >At 10:31 PM 1/16/2009, you wrote:
> >> >>Hi Mark,
> >> >>
> >> >>Thanks for the explanation. So if I understand correctly, the TelPak
> >> >> uses a newer hardware technology and can be used without the services
> >> >> of an MPI. Other than that they both do about the same thing...
> >> >> correct?
> >> >>
> >> >> > I should expand.
> >> >> >
> >> >> > There is a MAX chip in the TelePak that has acharge pump in it that
> >> >> > creates the RSR232 rail voltages.
> >> >> >
> >> >> > What this means is that you DO NOT need a multi-pak for this device
> >> >> > to work in a CoCo3 as the Tandy pack does.
> >> >
> >> >I've never known the Deluxe RS-232 Pak to not work in a CoCo 3
> >> >without an MPI.  There's a ROM in the pak which means you probably
> >> >can't use it at the same time a floppy controller is plugged into Any
> >> >CoCo unless you're using an MPI.
> >>
> >>It works if that teeny little Aztec 5 volt to +-12 volt switcher in it
> >> works, but the draw on the 5 volt line is more than the cc3 supply can do
> >> well.  I have seen several cc3s with blown fuses because that supply
> >> hiccuped.  The one in mine let out all the smoke and died a decade ago, so
> >> it works in an MPI only now.
> >
> >Why would the RS-232 pak need 12 volts?  The chips need 5v and are
> >few, plus the DC Modem Pak has more circuitry with the phone modem
> >portion so does it work on a CoCo 3?
>
>Because the signaling standards for RS-232 call for plus and minus 
>12 volts to
>be the swing level.  Therefore, they used a set of 1488-1489 level translator
>chips between the 6551 acia (or any other uart for that matter) and the
>output connector.
>
> >The reason I'm asking this is
> >because we're working on a simple RS-232 pak the size of a game pak
> >and I see nothing in it that should draw too much current from the
> >CoCo.  My hacked DC Modem pak works well on my CoCo 3 and someone
> >added the signal level converter ICs.
>
>And works without the plus and minus 12 volts when plugged into a coco3
>directly?  That has to be an extremely well balanced circuit, it should not
>normally.  Not to mention that since you don't have a disk system then,
>writing a driver for it in basic would be quite a coding exercise.
>
>So does mine, I made one of them out of a modem pack too, but it 
>only works in
>an MPI because those level translator chips need its plus and minus 12 volts,
>which the coco 3 does not supply, and which the older coco's only supplied
>very marginally, around +-9 volts IIRC.  That is enough to make it work 99.9%
>of the time, but leaves precious little over drive for noise margins and poor
>or long cabling.
>
>For all new designs, investigate the MAX-232 line of chips for that function,
>which contain their own charge pump level translators that are probably 500%
>more efficient than the Aztec mini-switcher in the RS-232 Deluxe pack ever
>thought of being.  That puppy ran HOT!  Or did in the 2 I have.  Neither have
>survived the ravages of age and 24/7 uptimes at the Heskett ranchette.


My hacked DC Modem Pak has a 1488 and 1489 and it has worked 
flawlessly from any CoCo 3 I've owned.  Odd.

Without the 1488/1489 chips - just a 6551, 27xx EPROM, 7404 and 74133 
should run from a 5v supply from the CoCo slot.  The CoCoNet pak will 
eventually send signals out over a 3.3v RS-232 bluetooth module.  I 
see no problem with it working with any CoCo 2 or 3 without an MPI.


-- 
Roger Taylor

http://www.wordofthedayonline.com