>    Hi All PICers !
>
> Wednesday December 18 1996 15:37,
> wsci@NET-MAGIC.NET wrote in PICLIST:
>
>  w> At 6:06 PM 12/18/96, J. Cabral wrote:
>  w>
>  >> I know that there is a simple circuit (without using MAX232
>  >> or 4188/4189) to convert RS232 TTL to RS232 C. The hardware
>  >> for communicating from the PC to the PIC is quite
>  >> simple! The circuit for communicating from the PIC to the
>  >> PC is more complicated (I can't remmember it!) it has a
>  >> MOSFET and same zenners. All the hardware needed was once
>  >> published in ELEKTOR, but I can't seem to find it! Does
>  >> anybody knows the circuit?
>  w>
>  w> do you have a negative supply?
>
>  It not necessary if you use TxD and RxD.
>
>                             e ----+5v
>    RxD_TTL------/\/\/\--- b    p-n-p transistor
>                  R1          c ----------------------- RxD_RS232
>                              |
>                               \
>                               / R2
>                               \
>                               /
>                              |_________|\|___________ TxD_RS232
>                            ______      |/|   |
>                            ______ C1         |
>                              |               |
>                             _|_              |
>                                              |
>    TxD_TTL ----------------------------------
>
>
> R1 - 10k-100k, R2 - 300-4k7, C1 - 10-100uFx16v
>
>    Best Wishes, Alex Torres.
>    Kharkov, Ukraine, exUSSR.
>    E-Mail To : altor@cook.kharkov.ua   via InterNet
>                or 2:461/28             via FidoNet
>
> --- GoldED 2.50.A0531+
>
>

None of it's necessary. I've always gotten away without any TTL to RS232C
circuitry, even with a 3V PIC. PC serial ports seem happy to accept
TTL logic levels, although you have to remember that they're the
other way up.

Brian Reilly