[OZAPRS] Small GPS

[James Cameron]

On Mon, Jan 10, 2011 at 10:29:52AM +1000, Andrew Rich wrote:
> I think from memory RS232 is zero is negative volts ?

No, a logic zero is positive on TxD and RxD.

Control signals are logically inverted though, you may be confused with
them.

> And a positive in RS232 is above x volts
> That is how GARMIN get away with the TTL

That's inverted TTL.  Did that on http://quozl.linux.org.au/ts/ where a
PIC output pin is connected directly to RxD on an RS-232 serial port.
The code inverts the bits as they are transmitted, see tx_byte in
ds1820.asm.

The risk of using TTL output to drive RS-232 RxD is that the RS-232
standard doesn't define what 0V means.  Usually works.

-- 
James Cameron
http://quozl.linux.org.au/