Texas Instruments MSC1210 manual Timer 2 in Auto-Reload Mode

Using Timer 2

TR2 (bit 2)— Timer 1 Run Control. This bit enables/disables the operation of Timer 2. Halting this timer will preserve the current count in TH2, TL2.

0 = Timer 2 is halted.

1 = Timer 2 is enabled.

C/T (bit 1)— Counter/Timer Select. This bit determines whether Timer 2 will function as a timer or counter. Independent of this bit, Timer 2 runs at 2 clocks per tick when used in baud rate generator mode.

0 = Timer 2 functions as a timer. The speed of Timer 2 is determined by the T2M bit (CKCON.5).

1 = Timer 2 will count negative transitions on the T2 pin (P1.0).

CP/RL2 (bit 0)— Capture/Reload Select. This bit determines whether the capture or reload function will be used for Timer 2. If either RCLK or TCLK is set, this bit will not function and the timer will function in an auto-reload mode following each overflow.

0 = Auto-reloads will occur when Timer 2 overflows or a falling edge is detected on T2EX if EXEN2 = 1.

1 = Timer 2 captures will occur when a falling edge is detected on T2EX if EXEN2 = 1.

8.5.2Timer 2 in Auto-Reload Mode

The first mode in which Timer 2 may be used is auto-reload. The auto-reload mode functions just like Timer 0 and Timer 1 in auto-reload mode, except that the Timer 2 auto-reload mode performs a full 16-bit reload (recall that Timer 0 and Timer 1 only have 8-bit reload values). When a reload occurs, the value of TH2 is reloaded with the value contained in RCAP2H, and the value of TL2 is reloaded with the value contained in RCAP2L.

To operate Timer 2 in auto-reload mode, the CP/RL2 bit (T2CON.0) must be clear. In this mode, Timer 2 (TH2/TL2) is reloaded with the reload value (RCAP2H/RCAP2L) whenever Timer 2 overflows; that is to say, whenever Timer 2 overflows from FFFFH back to 0000H. An overflow of Timer 2 causes the TF2 bit to be set, which causes an interrupt to be triggered (if Timer 2 inter- rupt is enabled). Note that TF2 will not be set on an overflow condition if either RCLK or TCLK (T2CON.5 or T2CON.4) are set.

Additionally, by also setting EXEN2 (T2CON.3), a reload will also occur when- ever a 1−0 transition is detected on T2EX (P1.1). A reload that occurs as a re- sult of such a transition causes the EXF2 (T2CON.6) flag to be set, triggering a Timer 2 interrupt, if enabled.

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