Fingerprint sensor RS232 communication

[sohailkhanonline]

Another point is this that you can never achieve baud rate of 9600 with 4 Mhz clock
I prefer you use hardware UART
transmit RC6
receive RC7
then write the interrupt service routine and in that routing use getc for taking variable from buffer and assign it immediately
make a user defined function where you can use
while (TRUE)
{
and when all the characters are recieved in you string define a break statement
}

I prefer you use 20Mhz HS oscillator
and MAX232 in b/w ur uC & finger print module
I hope it helps
_________________
sohail khan

[Depner]

Hi sohailkhanonline,
I'm already using Hardware UART. But if I'll use Max3232, then I must switch to sw, because hw. can not invert. As far as I know that's needed for the level translators.
Thanks for the tip for the Xtal. Now this is just a demo board, on the final application then I'll use 20 Mhz xtal.

[Ttelmah]

Er.
The serial hardware lines are _always_ inverted. They correctly give the standard signals to feed buffer chips like the MAX3232. This is the standard for hardware UART lines.
What they can't do is go to the non standard +ve logic mode, needed if you feed an RS232 line _without_ a buffer.

Best Wishes

[Depner]

So, it's working. No level converters, no nothing. It _is_ TTL levels. I jumped on it with an oscilloscope, and there were some really beautifull 5 V signals.
The problem was a little wiring issue... I tried it with a tiny code, it is recognising the fingerprints very good!
Now comes the programming. This is a very interesting project. I will read through the forum, 'cause I've got some questions about the rs-232 communication. If I won't find the answers, I will ask for your help a little bit.