RS232 pin.4 and pin.8

Dear All,
The pin.4 and pin.8 are not Tx or Rx of RS232, why I can
trigger RS232 directly by short them ?

Best regards,
Boki.

 

Subject: RS232 pin.4 and pin.8

I'm assuming you're talking about a DB-9 connector. Pin 4 is Data Terminal
Ready (DTR), and pin 8 is Clear To Send (CTS). The software you're using is
apparently telling the other side the Data Terminal is Ready, and when you
short the two, your software is noticing that the other side is sending that
it's Clear To Send.

You've got to back up the truck a bit here. First, on a hardware level, all
you're talking about is I/O port locations. You can read pin status by
bit-banging the ports. The trick is to get the UART to do the job of sending
and receiving serial transmissions.

Go to the library and borrow or buy a copy of "Serial Port Complete" by Jan
Axelson. There's a wealth of information in there for newbies on RS-232,
including software and drivers for BASIC, C, and Visual Basic. It's a bargain
if you're doing any hardware interface or programming with serial ports. If
you're in a hurry, go to the website for the book

http://www.lvr.com/serport.htm

and read some of the links. You'll learn what you need to know to do what you
want.

If all you want to do is read logic level of a few lines, you should be able to
do that quite easily. It should be especially easy if you use DOS with C on an
older PC. Also, the RS-232 port is pretty much goofproof. It's very difficult
to smoke it (although not imposible). However, if you're interfacing to +5V/0V
logic, it's a lot more likely you'll smoke some of that stuff.

Do a little reading first. You'll have a more enjoyable ride if you know
something about what you're doing.

Good luck
Chris

 

You really need to start specifying if you are using a D-9 or
D-25 type of connector for the pin numbers to make much sense.

 

Dear Chris,
I got it, thank you very much.

Best regards,
Boki.