[Coco] RS-232 Pak voltages

[K. Pruitt]

----- Original Message ----- 
From: "Gene Heskett"
To: <coco at maltedmedia.com>
Sent: Wednesday, April 08, 2015 5:09 AM
Subject: Re: [Coco] RS-232 Pak voltages


> On Wednesday 08 April 2015 03:23:39 K. Pruitt wrote:
>> Perhaps somebody knows this off hand:
>>
>> What should the voltage be on the DTR and RTS pins of the Tandy RS-232
>> Pak?
>>
>> I'm reading 1/10th of a volt.  Is it supposed to be that low?  I'm
>> fairly certain I am measuring it correctly.  Though I won't rule that
>> out as a potential issue.
>
> The little psu/convertor is duff, or the tx side (mc1488/mc1489 I can
> never recall which is which and both are easily blown by a long printer
> cable and a nearby lightning strikes emp.) driver chip is blown. If you
> have an MPI, and the convertor is duff you can remove the convertor and
> feed it from the MPI.
>
> But, I'd check the output of the convertor first, just in case one of the
> mc148x chips is blown.  They have not historically been a chipset noted
> for longevity in an abusive situation.  I don't recall that it makes the
> full 12 volts in both polarities, but anything above 8 volts is
> generally usable.
>
>> Thanks
>
> Cheers, Gene Heskett
> -- 
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>


Thanks Gene.  I tested it out with a modem and it works fine.  I'm measuring
the voltages from the pins, and not internally.
I'm getting normal voltages elsewhere so that is why I am assuming that I am
testing it correctly.  I found the datasheet for the 6551 chip and that has
been helpful.  The darn thing works, so I guess I should stop trying to
break it before I succeed.