I have been playing with some wireless modems that are RS232. I was thinking they should should be plug and play with my FTDI cable right? The cable is 5V and the modems are 5V and so are the rx/tx so I dont need a level converter right? I am trying to get them to communicate with the software used to program them with no luck. I swapped the rx/tx lines with no luck there either. Do I need to buy a USB to RS232 converter?
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RS-232 is +/- 12v, and a "1" is when the TX line is negative (reverse the standard TTL sense).
If the modems are some form of bastardized "+5v RS-232" then you can _safely_ connect them but you may need to invert the logic sense to read the data. In this case you will need a hardware inverter; just reversing the incoming bits won't work because the start bit will have the wrong sense too -- the UART won't know when to begin. (If the modems are "5v RS-232 compatible" then they are *not* safe; they will use +/-5v and the -5v will harm Ardu circuits.)
Replies
Neil -
Its been a couple of years - but were you ever successful with this integration effort? I am considering a similar type solution.
If the modems are 5V then they are not RS-232.
RS-232 is +/- 12v, and a "1" is when the TX line is negative (reverse the standard TTL sense).
If the modems are some form of bastardized "+5v RS-232" then you can _safely_ connect them but you may need to invert the logic sense to read the data. In this case you will need a hardware inverter; just reversing the incoming bits won't work because the start bit will have the wrong sense too -- the UART won't know when to begin. (If the modems are "5v RS-232 compatible" then they are *not* safe; they will use +/-5v and the -5v will harm Ardu circuits.)