RS-232 Logic Levels

We are creating our own version of the beagle board and I need to add
a second RS232 port. I plan to use UART2 for this. I'm a little
confused by the datasheet for the SN65C3221EPWR RS232 Line Driver. I
would prefer to use logic levels of +-12v due to the need for a longer
cable. Looking at the datasheet it seems like the SN65C3221EPWR used
in the REV C4 board may be operating at +-5V for the RX and TX lines.
Is this the case? Do I need to switch to a MAX232 in order to get the
12v I want or is this chip capable of outputting and receiving +-12v?

If you are connecting on a short cable to a PC, the 5V is more than enough. But, if 12V is required, then you need to find another part.

Gerald

In message <19813680-7f5d-404a-85ac-b3295b6c6564@p3g2000vbv.googlegroups.com>

We are creating our own version of the beagle board and I need to add
a second RS232 port. I plan to use UART2 for this. I'm a little
confused by the datasheet for the SN65C3221EPWR RS232 Line Driver. I
would prefer to use logic levels of +-12v due to the need for a longer
cable. Looking at the datasheet it seems like the SN65C3221EPWR used
in the REV C4 board may be operating at +-5V for the RX and TX lines.
Is this the case? Do I need to switch to a MAX232 in order to get the
12v I want or is this chip capable of outputting and receiving +-12v?

You just may find that +-5V works /better/ on long lines than +-12V
because the signals spend less time slewing between levels.

If you have trouble driving lines of the length you need at the speed
you need, you're way out of the RS232 specification. As always when
you use something beyond its specification, you're on your own, and
you shouldn't be surprised when it doesn't work.

For driving long lines with a serial signal, consider RS485.

Dave