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Serial interrupts on Mx2 chip

Sundeep Subbarau

Hi
This question is about serial interrupts on the 8051 based extended memory chip (P87C51Mx2).

The transmit interrupt TI_0 is supposed to be set when a character is written to S0BUF. This is not happening.
My initialization settings are as follows (I'm initializing both the UART channels)

T2CON = 0x30;
RCAP2H = 0xFF; // BAUD for UART0 - 9600
RCAP2L = 0xB8;

S0CON = 0x50;
S1CON = 0x50;

TXD   = 1;
RXD   = 1;
TXD1  = 1;
RXD1  = 1;
ES0   = 1;
ES1   = 1;

S0STAT = 0x00;
S1STAT = 0x00;

TR2 = 1;

BRGCON = 0x00; //UART1 baud - 38400
BRGR1 = 0x01;
BRGR0 = 0x10;
BRGCON = 0x01;


I'm setting the bits TI_0 or TI_1 when I've data to transmit and resetting it in the ISR. But what I observe is that the ISR is entered only once and never again!

The processor runs at 6 clock mode and 11.0592 MHz oscillator frequency.

Any help would be appreciated.

warm regards,
Sundeep M S

  • 0

    It would be easier to answer if you would show your ISR

    Erik

  • 0 in reply to erik malund

    Hi Erik,
    My ISR looks like this :

    void             //Return: Nothing
H_DC_INT_serial0_isr
(   void    )  interrupt 4 using 1 //UART0
{
    if (TI)
    {
        TI = 0;
        S0BUF = char_from_an_array_I_have_filled_earlier;
     }
}

    similarly I've for RI and also for UART1 (interrupt 10 using 1)

    -Sandy

  • 0 in reply to Sundeep Subbarau

    I'm setting the bits TI_0 or TI_1 when I've data to transmit and resetting it in the ISR. But what I observe is that the ISR is entered only once and never again!

    observe, how

    Erik

  • 0 in reply to erik malund

    I'm running the program on a simulator.

    The ISR has a breakpoint at it's entry point and I can see that the breakpoint is reached the first time to transmit the first character (I've 10 characters in my array).
    The S0BUF is loaded in the ISR and I expect that TI_0 is set so that the next character in my array is loaded to S0BUF and so on.

    The breakpoint is never reached after the first transmission.

    -Sandy

  • 0 in reply to erik malund

    Sundeep,

    I am not familiar with this chip, but is it not the case that TI and RI are associated with SBUF. Whereas, I would expect S0BUF to be associated with TI_0 and RI_0.

    If your are setting TI to get your ISR going then it will be invoked once. However, on completion of the transmission from S0BUF, it will be TI_0 that gets set not TI.

    Could it be, therefore, that you are also not using the correct interrupt number?

  • 0 in reply to Sundeep Subbarau

    The S0BUF is loaded in the ISR and I expect that TI_0 is set so that the next character in my array is loaded to S0BUF and so on.
    your expectation is correct, TI_0 should be set on completion of the transmission.

    Based on the above, your problem is not S0BUF/TI, but something else.
    Possibilities:
    1)the interrupt get disabled (check IE)
    2)the progrem gets hung elsewhere
    3)the simulator - It is a simulator not the real thing - does not simulate TI_0 correctly due to setup or malfunction.
    4) I tend to recall that in the MX you can redirect TI interrupts to an unique vector, leaving the standard vector for RI only. try making an ISR for that vector and see if that is wwhere you go.

    Erik