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Keil Variable declaration help

Roy Thomas

Actually on the external interrupt from port,I want to read the timer 2 value into a variable.(TH2 and TL2).
suppose I declare a variable
unsigned int timer2_val;
How can I move TL2 and TH2 into lower and upper nibble of timer2_val, so that I can treat Timer2 value as a single variable.
Weather keil has any declaration for assigning the lower byte or higher byte of a unsigned int to any hardware register or something like that.
I am a beginner in C.
Cygnalroy

Parents
  • 0 in reply to clever dick

    hi,

    timer2_val = (TH2*256)+TL2
or
timer2_val = (TH2<<8)|TL2

    Well, but just remember that you should stop the timer before read these registers otherwise you may obtain wrong values. It is because reading of integer value is split into two reading of bytes (chars) due 8051 8-bit architecture. And if timer run then there is a chance that TL2 and TH2 registers change their values between these two readings.

    Regards,
    Oleg

Reply
  • 0 in reply to clever dick

    hi,

    timer2_val = (TH2*256)+TL2
or
timer2_val = (TH2<<8)|TL2

    Well, but just remember that you should stop the timer before read these registers otherwise you may obtain wrong values. It is because reading of integer value is split into two reading of bytes (chars) due 8051 8-bit architecture. And if timer run then there is a chance that TL2 and TH2 registers change their values between these two readings.

    Regards,
    Oleg

Children
  • 0 in reply to Oleg Sergeev

    Well, but just remember that you should stop the timer before read these registers otherwise you may obtain wrong values. It is because reading of integer value is split into two reading of bytes (chars) due 8051 8-bit architecture. And if timer run then there is a chance that TL2 and TH2 registers change their values between these two readings.

    Sage advice!