I am using all of my RS232 ports and want to control one more component via RS232. What happens if hook of a y splitter to send commands to two different pieces of equipment (AV receiver and subwoofer amp). I am assuming that if you send a command to the AV receiver it will work but but what happens when that same command is sent to subwoofer amp? Will this cause problems if it is two completely different pieces of equipment by different manufacturers with different protocols?

FYI - this is the type of y splitter i am talking about

[Link: cgi.ebay.com]

You can not Y-Split an RS232 serial cable. Might get away on the transmit side depending on the RS232 receiver chip design, but probably not (Electrical loading as RS232 receivers are not tristate).

Lets just say for arguments sake that xmit was OK. Now two pieces of equipment choose to answer the command they see. Device 1 with a proper response if it saw something it understod, Device 2 with some error response. Ball game over the input will be garbled junk.

RS-232 is intended to be a point to point protocol, not a bus protocol. It is like having two batters simultaneously stepping up to the plate.

If you are lucky, commands to one device will be invalid and harmlessly ignored by the other device. If these devices talk back, your program will need to be able to determine which device is talking and hope that they do not attempt to reply simultaneously because both replies will be garbled.

This is not a good idea.

About every two weeks, somebody posts on here about splitting or sharing RS232 between multiple devices.  Take a look at this...

I have seen some products which stuck on invalid RS232 commands (Optoma projectors if I recall correctly)