[Coco] Telepak RS232 Pak

[Tim Fadden]

Actually 12v is the median voltage. The maximum is 25v and the minimum 
is 3v. Depending on cable lingths, quality, etc, 5v will work just fine. 
All-be-it it's at the low end of the specs.

Good right-up here: 
http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html#anchor1181130

Also found this one here: http://www.omega.com/TechRef/pdf/RS-232.pdf


TRANSMITTED SIGNAL
VOLTAGE LEVELS:
Binary 0: +5 to +15 Vdc
(called a “space” or “on”)
Binary 1: -5 to -15 Vdc
(called a “mark” or “off”)

RECEIVED SIGNAL
VOLTAGE LEVELS:
Binary 0: +3 to +13 Vdc
Binary 1: -3 to -13 Vdc


Google is smart, use it! ha ha ha Too bad you have to weed out so much 
advertising to get to the good stuff! Hasn't always been that way.

Cheers!

Tim

etc, Gene Heskett 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.
>
>