Kinda sorta maybe possibly. I had thought about using one of the
variants of max232, instead of the 3 transistor hack. But in the end,
the 3 transistors is probably the cheapest and simplest circuit to make
a tpdd work, and this new circuit with the part that Rick Shear
identified, really does seem to be just like the original cable. I
haven't used a scope to compare the actual signals, but I have a scope
and an original cable so I could. I think I'll do that.
It was a while ago so I might have some of this wrong, but what I think
I remember was most of those ttl to rs232 level-shifter chips don't have
3 channels, and so you can't handle all 3 lines that the three
transistors handle, you wouldn't get DSR/DTR. And most of them also need
auxiliary caps for the charge pump to parasite power from the rs232
lines which do not actually deliver any power to speak of. There are
special ones that have their own caps built in, and there are special
ones with more channels, or you could use multiple regular ones. So, you
might only be trading 3 transistors for a max232 and two caps, or a big
expensive special max232 etc.
I still wouldn't mind tryng it just for the heck of it. The result would
be a cable that should be more technically correct, and so and more
reliable, when used with other random generic serial ports besides the
one on a model 100-200, yet still work perfectly on a model 100-200
(which has pullup resistors, which the original tpdd cable circuit banks
on).
But I don't think the result would be any cheaper or simpler to make.
--
bkw
On 7/17/19 10:59 AM, Kurt McCullum wrote:
Brian,
I noticed you have a new DB25 PCB on Osh Park. I suspect the whole
TPDD cable was intended to take a TTL level floppy drive and bring it
to a standard RS-232 level. I'm wondering if that same PCB could be
used with one of the inexpensive TTL level FTDI USB to serial
converters to create a PC to Model-T cable? The only problem I see is
that the TTL level FTDI cables are all 6 wire and don't seem to have
the DTR wire. But I suspect that could be hard wired some how.
Kurt
On Wed, Jul 10, 2019, at 11:28 PM, Brian K. White wrote:
I finally did the version of this that I had envisioned.
https://oshpark.com/shared_projects/Sk27mJwq
