Help please on Observer / Observable and Serial Communications!

Question

Help!
I have a project where I need a java application to talk to some test equipment via the serial port. I have studied the java comm api and played around with the SerialDemo example which I used to model my code.
I have a SeialConnection class which is very similar to the example except I made it to extend Observable and I have it notify observers when data is detected on the serial port.
I created a second class which extends Obserable which communicates with the SerialConnection and implemented the observer interface. This class process the incomming and outgoing data and provides some higher level methods, like getSerialNumber(), for my application to use. The application frame is an Observer of this class so the GUI can show the status as well.
An example method from this class:
private String Get590AROMString() {
SendString("EZR-V"); //Send a command to the s.p.
serialConnection.pause(750); //Basically a sleep(750)
return ROMVersion; //Return the data from update()
Excerpt from update method:
// If return from serialConnection starts with VER: parse the RV and SN.
if(T.startsWith("VER:")) {
ROMVersion = new String(T.substring(0,T.indexOf('~')));
SpeciesName = new String(T.substring(T.indexOf('~')+2));
return;
This works great when the test equipment sends a message or when the user selects a command from the program interface. My problem is when I try to send a command to the serial port from within the update method of the observer. There are instances where a result from the serial port needs to initiate another request for information.
Here is a fragment from the update method of the application frame:
public void update(Observable obs, Object obj) {
DensTalkStatus DTS;
if( obs==DT ) {
DTS = (DensTalkStatus)obj;
else if(DTS.GetStatus()==DensTalkStatus.NOTIFY_ZEROOK) {
if(FIRSTCONNECT590A) {
GDD.GetDensimeterInfo(); // *** This is the Request
GDD.SetDensID(EDM);
FIRSTCONNECT590A = false;
When I make a request for additional information from the serial port within the update method I get nothing returned and the requested data arrives later after the update method has completed.
I do not know the fine details of how the javax.comm or observer/obserable works but it appears to me that my strategy can only process one command at a time.
Can anyone think of a way to allow the application's frame update method to request information and wait for the data to be ready?
Does anybody have an example of how to do this type of communications?
I am sorry for the length of this question... Thank you for your time.
Doug

Answer 1

I have not received any suggestions yet on an alternate method for this problem, but I have come up with a solution I think will work. I am posting it here so others who have the same problem can at least see what path I followed...
The basic problem seems to be that I am trying to have my observer ask for information that requires the same observer / observable thread to respond.. duh! :) To requst additional information from the serial port I need to move the requests out of the update() method to a different thread.
I implemented the SerialWorker class to make the request so the observer update() method could return normally without waiting for the result of the new request.
Doug