[Coco] Telepak RS232 Pak

[Gene Heskett]

On Saturday 17 January 2009, Roger Taylor wrote:
>At 11:49 AM 1/17/2009, you wrote:
>>On Saturday 17 January 2009, Roger Taylor wrote:
[...]

>>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.

And it will continue to work, until it has to face a genuine RS-232 interface 
in a 1974 printer. :)  A ttl level signal will not drive my old Xerox 
1650-ro, no response.  The coco's bit banger can though.

>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

I think RS-232 is a good protocol myself, and I see no reason to not use it at 
straight TTL logic levels with short runs of good shielded cabling.  Or to 
your bluetooth module on the same board, it makes absolutely perfect sense.
But we shouldn't call it a legit RS-232, its not.

If we don't tell the chips they aren't supposed to work, they usually will. :)  

I once needed a really fast 3/8 decoder for a cmos circuit that had about 28 
volts on it, so I used the 15 volt rated CD4xxx chip that was available.  I 
got sub 100ns rise and fall times out of it, at ntsc video speeds, with only 
a 10F temp rise.  It ran for several years that way, putting adjustable color 
and brightness outlines around the characters in an old 3m character 
generator at KRCR in Redding CA.

>see no problem with it working with any CoCo 2 or 3 without an MPI.

But where do you get a driver for it in a diskless scenario?  Or is the 
teletext rom still enabled?  I had forgotten that thing even exists...

-- 
Cheers, Gene
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