Texas Instruments MSC1210 - Manual (Page 89)

Using Timer 2
8-15
Timers
8.5.3 Timer 2 in Capture Mode
A new mode, specific to Timer 2, is called capture mode. As the name implies,
this mode captures the value of Timer 2 (TH2 and TL2) into the capture SFRs
(RCAP2H and RCAP2L). To put Timer 2 in capture mode, CP/RL2 (T2CON.0)
and EXEN2 (T2CON.3) must be set.
When configured as mentioned above, a capture occurs whenever a 1-0 tran-
sition is detected on T2EX (P1.1). At the moment the transition is detected, the
current values of TH2 and TL2 is copied into RCAP2H and RCAP2L, respec-
tively. At the same time, the EXF2 (T2CON.6) bit is set, which triggers an inter-
rupt, if Timer 2 interrupt is enabled.
Note:
Even in capture mode, an overflow of Timer 2 results in TF2 being set and
an interrupt being triggered.
Note:
Capture mode is an efficient way to measure the time between events. At the
moment that an event occurs, the current value of Timer 2 is copied into
RCAP2H/L. However, Timer 2 will not stop and an interrupt will be triggered.
Thus the interrupt routine must copy the value of RCAP2H/L to a temporary
holding variable without stopping Timer 2. When another capture occurs, the
interrupt can take the difference of the two values to determine the time tran-
spired. Again, the main advantage is that Timer 2 does not need to be
stopped to have its value read, as is the case with Timer 0 and Timer 1.