Hi!
I just got an STK500 development kit that I'm trying to understand how to use. If I don't use an external programmer, I'll have to use the RS232 port. The problem is that I don't have an RS232 port on my PC. I got a cheap PL2303 USB to RS232 converter, but this is just a USB to serial adapter with a DB9 connector. There is no voltage level converter built into this adapter.
To get the STK500 to work, I need a USB to Serial adapter, with a built in voltage converter. Does any of you know a cheap adapter that actually works as an RS232 port, with the correct voltage levels?
However, I have heard that some of these adapters do not produce the full, standard +12V/-12V swing on the output. Some are reported to swing from +5V to -5V, so look for the +/- 12V specification.
Hi,
Go down to your local computer tech/shop and buy a decent one.
Worth the cost, and you can take your laptop in to check if it loads.
If it doesn't do the job, you can take it back.
To get the STK500 to work, I need a USB to Serial adapter, with a built in voltage converter. Does any of you know a cheap adapter that actually works as an RS232 port, with the correct voltage levels?
Have you actually tried one of the 5v USB adapters and it failed?
zoomkat:
Have you actually tried one of the 5v USB adapters and it failed?
Yes, I've tried my USB to serial adapter with a DB9 connector at the end. Didn't work. I managed to borrow an expensive Aten USB to RS232 from my school, and it worked like a charm. I guess my adapter (PL2303) don't output negative voltage..
These are great http://store.sure-electronics.com/mb-cm13112 they give you the best of the best a real com port with the right voltage levels plus two ports that are 5 volt on one and 3.3 volt on the other
so you have a .
1 RS-232 at + - 13 volts USB to DB9 Female, USB to DB9 Male
2 A 5V CMOS Level
3 3.3V CMOS level
I got two of them about 5 years ago I just look over a Sure Electronic'e and they still sale them cost a little more now. I got mine both for $9 each there $14.80 now But it is very good CP2102 USB-RS232 Serial Convert Communication Module That works for anything you would ever need.
It comes apart so you can use just 5v and 3.3 cmos level.
hansibull:
Yes, I've tried my USB to serial adapter with a DB9 connector at the end. Didn't work. I managed to borrow an expensive Aten USB to RS232 from my school, and it worked like a charm. I guess my adapter (PL2303) don't output negative voltage..
Have you ever read up in order to comprehend what the RS-232 standard actually is?
The negative voltage is not the point; quite irrelevant in fact. The point is that the logic levels are inverted to what your USB to TTL converter and all UART chips and microcontrollers use.
The MAX232 and its derivatives not only contain the charge pumps to generate ±10 V - which is more than adequate to satisfy the standard - but invert the logic levels to suit. A MAX239 plus a USB to TTL chip such as the FT232 or CP2102 or PL2303 makes a complete USB to RS-232 adapter lead, usually moulded into the DB-25 or DE-9 housing.
Further, if you simply connect a common USB to TTL converter module directly to a DE-9 connector, you may be subjecting it to damaging voltages if the other device generates actual RS-232 levels.
Yep and then USB came along and they figured -5 to+5 was good and My JDM programer stopped working so we started add a battery or two to bring the level up But hick you'd think every one new a -3 or better is a 1 and +5 or better is a 0.
But even the people making computer boards never got it right.
A USB to TTL adapter should not have a DE-9 connector on the end.
Some of the USB/Serial chips (I think including the PL2303) have an option that outputs "inverted TTL": 0V/5V instead of "<-3/>+3" These will work with "many" (but not all) devices that expect real rs232. (I have fond memories of connecting up some mc1488 drivers to 0/5V instead of +/-12 in an attempt to get a board talking. It worked!)
In general, to get real-ish rs232 out of an adapter, you need to find one with at least two chips. Good luck figuring that out from an eBay item. (actually, I see a couple "usb rs232 max232" boards that have an obvious extra chip. No DB9, though...)
None of the "real" rs232 converters I have were "cheap", so I can't offer a particular recommendation.
westfw:
Some of the USB/Serial chips (I think including the PL2303) have an option that outputs "inverted TTL": 0V/5V instead of "<-3/>+3" These will work with "many" (but not all) devices that expect real rs232.
Yes, I thought of that and was researching it earlier today.
I cannot however, find any such option in the PL2303, so the concept of a single chip RS-232 adapter using it sounds very odd indeed and I am for the present, stumped. If the option was there, it would require a different driver configuration which would in itself be an implementation problem (unless it was controlled by a pin on the chip, and I see no evidence of that either).
westfw:
In general, to get real-ish rs232 out of an adapter, you need to find one with at least two chips.
