ST ST7 - Page 301

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10 - Second Application: a Sailing Computer
ld a, TBIC1HR /* Get new time */
ld Capture1.W.Low, a
ld a, TBIC1LR
ld Capture1.W.Low:1, a
}
BoatPeriod = Capture1.Long - LastCapture1 ; /* calculate time
difference */
LastCapture1 = Capture1.Long ; /* Remember this time for next
capture */
}
if ( TBSR & ( 1 << ICF2 ) ) /* Is this is a capture 2 interrupt ? */
{ /* yes */
asm
{
ld a, TBIC2HR /* Get new time */
ld Capture2.W.Low, a
ld a, TBIC2LR
ld Capture2.W.Low:1, a
}
WindPeriod = Capture2.Long - LastCapture2 ; /* calculate time
difference */
LastCapture2 = Capture2.Long ; /* Remember this time for next
capture */
}
if(TBSR&(1<<TOF)) /*Isthis is an overflow interrupt ? */
{ /* yes */
asm
{
ld a, TBCLR /* clear interrupt request */
}
Capture1.W.High++ ; /* Increment high order word */
Capture2.W.High++ ; /* on both channels */
}
}
All timer events trigger the same interrupt request. At the beginning of the function, the TBSR
status register is tested for one of the following three events:
 Capture 1 event
 Capture 2 event
 Timer overflow event
Once the originof the interrupt has been determined, the flag must be cleared. This is done by
reading the capture low register of the corresponding channel, or by reading the free-running
counter low register, for an overflow event.
As said above, the captured value is written to the low-order word of the capture variable
which is of type unsigned long. The overflow of the timer produces the incrementation of the