PC almost at standstill

[Paul]

My guess is someone with access (like a seagate tech) volunteered that
information to help techs with a specific issue. It sure would be fun
to know what all is available, though, if only to play around with stuff.

I have seen people solder on pin headers to routers in order to
repurpose them, but in those cases it was pretty clear it was just a
regular RS232 port on Linux firmware.

Jon

With the emphasis being, the serial port you solder on, is TTL level
rather than RS232. If you solder RS232 to one of those pin headers,
bad things will happen. TTL is for "local" interconnect, while
RS232 is for pieces of equipment separated by long distances,
with some measure of protection for short circuits and the like.
RS232 uses much higher voltages, which is why it's a bit of
a threat to some kinds of low voltage circuits (3.3V based).
For example, some unprotected GPIO, might not be able
to withstand RS232 voltages and survive.

So if you were to participate in such fun and games, you want
to make sure you have the right kind of serial adapter. The
two USB to RS232 I own, would not do. They're the wrong type.
I'd need to plop on a level translator, if I wanted to use those.

(I don't know if this is a "good one", but the adapter is about the
right shape...). The question here would be, where does the phantom
power come from, to run it ? I don't see anything to power the
low voltage side. Perhaps it is open collector TTL (pullup resistors
provided by the Device Under Test) ?

http://www.amazon.com/HOSSEN®-MAX23...809439&sr=8-2&keywords=ttl+to+rs232+converter

It's generally just better to buy a USB to TTL serial adapter instead,
as then you don't need a level translation step. Apparently, these
were originally intended for some kind of cellphone application.
But end up used for other projects as well (like the router
internal interface).

http://www.amazon.com/PL2303HX-RS23...09661&sr=1-1&keywords=usb+to+ttl+serial+cable

Paul

 

[Jon Danniken]

With the emphasis being, the serial port you solder on, is TTL level
rather than RS232. If you solder RS232 to one of those pin headers,
bad things will happen. TTL is for "local" interconnect, while
RS232 is for pieces of equipment separated by long distances,
with some measure of protection for short circuits and the like.
RS232 uses much higher voltages, which is why it's a bit of
a threat to some kinds of low voltage circuits (3.3V based).
For example, some unprotected GPIO, might not be able
to withstand RS232 voltages and survive.

So if you were to participate in such fun and games, you want
to make sure you have the right kind of serial adapter. The
two USB to RS232 I own, would not do. They're the wrong type.
I'd need to plop on a level translator, if I wanted to use those.

(I don't know if this is a "good one", but the adapter is about the
right shape...). The question here would be, where does the phantom
power come from, to run it ? I don't see anything to power the
low voltage side. Perhaps it is open collector TTL (pullup resistors
provided by the Device Under Test) ?

http://www.amazon.com/HOSSEN®-MAX23...809439&sr=8-2&keywords=ttl+to+rs232+converter


It's generally just better to buy a USB to TTL serial adapter instead,
as then you don't need a level translation step. Apparently, these
were originally intended for some kind of cellphone application.
But end up used for other projects as well (like the router
internal interface).

http://www.amazon.com/PL2303HX-RS23...09661&sr=1-1&keywords=usb+to+ttl+serial+cable

ul

I was lucky enough to get sent a couple MAX232 chips for evaluation from
Dallas, and have had fun with them in a few projectes. USB kind of put
a crimp on that, although I would imagine there are USB-Serial
convertors for cheap.

Jon

 

[Bob F]

(I don't know if this is a "good one", but the adapter is about the
right shape...). The question here would be, where does the phantom
power come from, to run it ? I don't see anything to power the
low voltage side. Perhaps it is open collector TTL (pullup resistors
provided by the Device Under Test) ?

http://www.amazon.com/HOSSEN®-MAX23...809439&sr=8-2&keywords=ttl+to+rs232+converter

My understanding, from many years ago, is that the MAx232 charges up capacitors,
then switches them from the battery to put the positive lead at gnd, and the
negative lead on the neg lead of another cap to charge it, producing the
negative voltage needed. All done at a high repetition rate.

 

[Paul]

My understanding, from many years ago, is that the MAx232 charges up capacitors,
then switches them from the battery to put the positive lead at gnd, and the
negative lead on the neg lead of another cap to charge it, producing the
negative voltage needed. All done at a high repetition rate.

That's a charge pump. I can understand it being used, to boost 5V supply
to +/- 12V for the RS232 outputs. But I don't know if it works the
other way (receive 12V signals, make 5V from them). People have implemented
various phantom power schemes, using the RS232 status signals.

http://www.maximintegrated.com/datasheet/index.mvp/id/1798

"particularly applications where ±12V is not available"

I thought that is what it used the charge pump for, was making
the RS232 +12 and -12, from a +5V input supply. In the diagram,
the doubler converts +5V to +10V (enough for RS232), while the
inverter stage makes -10V for the other rail.

http://www.maximintegrated.com/images/qv/1798.gif

I don't see it as being impossible to make 5V for some CMOS logic,
using the RS232 signals themselves as a power source. But it would
likely be some other family than MAX232.

Paul