RS232 Pin to Monitor to Detect Connection

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

Hello All,

I'll be attempting a full 9 pin implementation of RS232 soon and would like to be able to have the PIC detect when a DTE is connected. What pin should I monitor to detect that event? The DTR?

Also, on the TTL/CMOS side of the level-shifter, what will be the logic levels when connected and unconnected?

Thanks,

John

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

If I have a question about serial ports, I go here because it's got so
many links:
http://www.lvr.com/serport.htm

jecottrell · Joined: 16 Jan 2005 Posts: 559 Location: Tucson, AZ

PCM,

Thanks. I hadn't seen that site before, even though I have Serial Port Complete. I pulled that out and dusted it off and found alot of what I needed. (I had forgot it was in my book case.)

I went back to a simple 3 wire connection. Since it's for Small Burst Data (SBD), I shouldn't need any flow control and decided to keep it simple. However, I did rig up a Schottky w/ a series current limiting resistor and then a 3V zener to ground off the DTR line to the PIC to indicate when it's connected to the PC.

John