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bowen303
09-05-2008, 02:04 PM
I ran into a little trouble last night that I don't understand and it involves the rs-232 ports on the protoboard. It looks like I may have fried the RF engine board after hooking up another rs-232 to the protoboard. (i assume it is fried since portal doesn't see if for a nv reset or a image erase and it seems to heat up substantially when plugged in.) I am using a TTL to RS-232 converter board that comes out as 5V. I figured this was ok since I have hooked the proto board up to a pc db9 rs-232 connector with no ill effects. (Did i get lucky here?) Afterwards, i looked at the hardware sheet and I only see 3.3v listed for both uarts. Which in my mind means I will have to bring down the voltage before I try that again. Is this correct?

I guess also what puzzles me is I thought pc rs-232s could range from 3v to 12v depending on the manufacturer. Is there something different about a PCs port that would cause it not to blow the proto board?

Sorry about all the questions, I am really just trying to figure out what I did wrong and not make another 30 dollar mistake.:D

It probably makes no difference, but the ttl/rs232 board is female and the protoboard is female. I used the standard rs-232 cable and a gender changer to connect them. the ttl/rs232 device converts a 3.3v from a PIC to 5v rs-232 and that is what I connected.

msellers
09-05-2008, 02:34 PM
The RF engine has two TTL level (3.3V) UARTS. When using the RF engine in one of our boards with a DB-9 RS-232 connection, the conversion is done with a TI 232 driver chip for you. If you need to connect both UARTs to RS-232, you would have to add a driver to do the conversion for the second port. If you are interfacing the RF engine to another processor with 5V I/O, you can use a dual rail buffer like the TI SN74LVC8T245 8-channel version and skip the RS-232 conversion process.

The i/o on the RF engine is not 5V tolerant so any drivers connected need to be 3.3V on the TTL side.

UPDATE: the 2 and 4 channel TI parts are limited to 3.3V, only the 8 channel part can be used with 5V on one rail to convert 5v signals to 3.3v