[oopic] Re: oSerialH on ooPIC-R, TTL-Level or true RS232?

--- In oopic@yahoogroups.com, "design.wonk" <design.wonk@...> wrote:
>
> Just curious... How is the oooPIC-R able to communicate with my PC
> using a serial cable with no inverter?

The logic levels (0 and 1) are corrected for RS232 definitions of mark
and space by inverting the TTL signals from the uC. The PC has level
changers as well inverting the signal from the SuperIO chip (the
likely chip).

The unfortunate thing is that the OOPic-R (and -C) inverted signals
are NOT really RS232 voltage levels. So, while the OOPic-R can talk
to a PC, there are a number of things it can't talk to. Some
USB->Serial cables, for example. A real level shifter will come a lot
closer to RS232 voltage levels - usually on the lower side of the
voltage range but definitely both above and below ground.

Nevertheless, it all kind of works out.

Richard

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