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    <p>The problem is that both your send and receive functions are polled and blocking. When you call the receive function, it will only return after a complete message is received. Dito for the send function, but in case of send the duration is propably shorter (your program will propably only call send when there is a message to be sent, while receive can wait for days before a message arrives.</p> <p>If you require asynchronous commmunication, the best is to use interrupt based communications; at least for the receive and ideally for both send and receive.</p> <p>It is also possible to impement this using polled communications, but then you need to write a function which checks if a character is available for receive (or if tx-empty), to read/write the next character from/to the buffer.</p> <p>The advantages of interrupt based communication are:</p> <ul> <li>full duplex</li> <li>less cpu time is used (no wait loops necessary)</li> <li>less power (it allows the cpu to go to a low power/standby mode, with wakeup on interrupt; polling always requires full power)</li> </ul> <p>As a first step I advise you to implement (or get) a interrupt based receive; even when the transmit function is still blocked, it will allow full duplex operation with minimal effort. If you haven't got a os (rtos/scheduler) you'll have to think of a synchronisation mechanism. The simplest form is for your receive to handle a message if there is one available, and to return immediately if there isn't a (complete) message.</p> <p>good luck.</p> <p><strong>Edit after comments</strong> On a message-by-message basis, things may seem to work if the desktop is reacting on messages sent by the controller. If your controller has a large FIFO buffer (i.e. 64 bytes) on the receive, this may work. Most controllers I know haven't got this. Many have only a single character buffer. You can detect this using an OVERFLOW bit in the registers; if this is set, then characters were lost on receive. </p> <p>Some usecases: * you want to send 2 messages in one go (say: init + do_something). The pc responds to the first msg, but the controller is still sending and drops most of the data. * PC starts sending before controller is executing the receive() function. Data at the beginning of the packet may get lost * any drop in communication may cause a deadlock (i.e. controller and desktop are both waiting for the other end to send something.</p> <p>So to diagnose: check the overflow bit. If it is set, you have lost data and you need to work on the interrupt functions. If possible, monitor both sides (at least the state; a blink a led for send, and one for receive for instance).</p> <p>A rs232 monitor may help you (you'll need some additional ports for this. There are many (including freeware) applications which can monitor multiple rs232 ports and provide timestamps. So you can observe the order of communications. Google found me : <a href="http://www.commfront.com/RS232_Protocol_Analyzer_Monitor/RS232-Analyzer.htm" rel="nofollow noreferrer">link</a>; I've used several similar utilities in the past years.</p>
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    1. POHow do I continuously send and receive with wireless serial-port in 8051?
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    1. COThank you so much for your suggestion Adriaan. But I'm confused. I had a hunch that it may not be working because of the blocking aspect but I figured that the way I'd written my programs would have gotten around it. See I make the controller send a msg while the desktop program is waiting on it with a Receive() Then the desktop program checks the msg sees if it's acceptable (all this while the controller program is waiting to Receive) and then sends a msg signaling acceptance or rejection of the msg. The Receive() in the controller that was blocked is now unblocked isn't it?
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    2. COSo shouldn't it just proceed with the rest of the code? That is check whether the received msg is for acceptance or rejection (During this time the desktop computer is waiting with a blocked Receive) and then send the msg again? I'm sure asynchronous communication would solve this probelem like you said, but I'm on a bit of a deadline with this project and I've never tried asynchronous comm. before so I would really really appreciate if you could help solve this with synchronous!
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    3. COsee edit in answer.
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