Sharing Max232 with two pics?

[zx81sp]

I have a board with two 16F628A and one Max233, and I want to share it with the two PICs.

Apparently it works ok but one of the PICs has been damaged (I can't reflash it), I've tried with another, first time works ok but when I try to reflash it fails (broken again).

The pics does not use the RS232 at same time for send data, and I assume that when they receive it's not problem to share the signal.

The first PIC uses a 20Mhz OSC and I'm using this code:

OUTPUT SERIAL_OUT 'make the pin an output
PAUSE 125 'don't know why, but whitout this pause does not work
SEROUT SERIAL_OUT,BPS,[126,V,"0000"] 'send data
INPUT SERIAL_OUT 'mak pin an input

The second PIC uses a internal 4Mhz OSC and don't know why, but same code does not works, so I use directly this code:

SEROUT SERIAL_OUT,BPS,[126,V,"1111"] 'send data

and this is the PIC that always end broken (it works ok, but I can't reflash it).

May be damaged because the SERIAL_OUT pin is allways output?

[Luckyborg]

I would either switch the pin to an input when not transmitting or probably put a couple diodes in line with the 2 micros and a pull up resistor before the max233. Haven't built it, so I might have the diodes backwards.

David

[Bruce]

Why not just use one of the OPEN baud modes? This leaves the TX pin set to input
after the transmission is complete.

[zx81sp]

Why not just use one of the OPEN baud modes? This leaves the TX pin set to input
after the transmission is complete.

With OPEN transmission does not works, nothing happens, I think that mode is for direct connection to the PC.

I'v solved the mistery of the broken PICs (just a programmer bug), anyway if someone have a better idea to share the MAX233, would be appreciated.

Thks

[mister_e]

OPEN mode work if you use a good enough pull-up resistor for true mode...

[zx81sp]

OPEN mode work if you use a good enough pull-up resistor for true mode...

I can try it, would be enough a 47k resistor?