RS232 not working, probably a electrical problem

[petfo]

hi!

i use a PLCC44 pic18f452 with a intersil SO16 max232 line driver, my bootlaoder isn't working (doesn't recognize the CPU) and so i think this coud be an electical problem either with the MAX232 or with the line itself.
when i measure pin13 of MAX232 (TX on the MAX232 side) it has 0V.
same with ground ;)
and RX (pin14 on the MAX) it has ~ -8V.

maybe its a problem with the cpu itself, i looked with a scope at the OSC1 and OSC2 pins and it looked kinda like a pseudo sawtooth with a freq of 20MHz. (i'm using a 20MHz crytal) but Vdd is @ 5V and Vss @ 0V

i dunno y, but everytime i try to use SMD packages my vanilla and proven circtuis stop working right :(

[petfo]

i'm using 1uFs elect. caps and a groundplane, the 7805C doesn't swing(vcc line is clean and stable @ 5V).

[Beginner]

Hi,

have you tried an rs232 testprogramm?
so you can say that the communication is working correct?
when it's work, than there is a timing problem with your bootloader and your baud rate.

i think so, i had such a problem with a 16f876

regards

Beginner

[ckielstra]

You say your RS-232 line is not working, but in this same post you are checking your oscillator as well. Why? Are you doubting your processor is running at all?

I would suggest to start at the basics again.
1) Make sure your processor is running, for example toggle an output pin every second so you can check this with a LED or voltage meter.
2) Output a continuous stream of data over the RS-232 transmit and try to receive this on the PC. This will prove your baudrate settings are correct and your transmit hardware is correct.
3) Prove your RS-232 receive hardware is correct by writing a small test program that waits for data on the Rx and outputs it directly on the tx again.


I don't have the schematics for the MAX232 here, but pin13 is supposed to be carrying RS232 voltage levels? If yes, then your 0V here is suspect to error, this is an undefined voltage in RS-232.