Question

I have to send file byte-by-byte to serially connected AT89s52 from computer (VB.NET).
Every sended byte have some job to do in microcontroller what require some time.
Here is relevant part of my C code to receiving bytes:

SCON = 0x50;
TMOD = 0x20; // timer 1, mode 2, 8-bit reload
TH1  = 0xFD; // reload value for 9600 baud
TR1  = 1;
TI   = 1;

again:

        while(RI!=0)
        {
            P1=SBUF;          // show data on led's
            RI=0;
            receivedBytes++;
        }

        if (key1==0)
        {
            goto exitreceive; // break receiving
        }

        show_lcd_received_bytes(receivedBytes); 
        // here is one more loop 
        // with different duration for every byte
        goto again;

And here is VB.NET code for sending bytes:

    For a As Integer = 1 To 10
        For t As Integer = 0 To 255
            SerialPort1.Write(Chr(t))
        Next t
    Next a

Problem is that mC have some job to do after every received byte and VB.NET don’t know for that and send bytes too fast so in mC finishes just a part of all bytes (about 10%).
I can incorporate “Sleep(20)” in VB loop ant then thing will work but I have many of wasted time because every byte need different time to process and that would be unacceptable slow communication.

Now, my question is if 8051 can set some busy status on UART which VB can read before sending to decide to send byte or not.
Or how otherwise to setup such communication as described?
I also try to receive bytes with serial interrupt on mC side with same results.

Hardware is surely OK because I can send data to computer well (as expected).

Answer 1

Your problem is architectural. Don’t try to do processing on the received data in the interrupt that handles byte Rx. Have your byte Rx interrupt only copy the received byte to a separate Rx data buffer, and have a background task that does the actual processing of the incoming data without blocking the Rx interrupt handler. If you can’t keep up due to overall throughput issue, then RTS/CTS flow control is the appropriate mechanism. For example, when your Rx buffer gets 90% full, deassert the flow control signal to pause the transmit side.