Electronic Circuits and Tutorials
Additional Features in 8052

8052 Microcontroller Tutorial
Timer 2 in Auto Reload Mode

Author: Craig Steiner

Book: The 8051/8052 Microcontroller:
         Architecture, Assembly Language, And Hardware Interfacing (Paperback)


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 will be reloaded with the value contained in RCAP2H and the value of TL2 will be 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) will be 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 will cause the TF2 bit to be set, which will cause an interrupt to be triggered, if Timer 2 interrupt 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 whenever a 1-0 transition is detected on T2EX (P1.1). A reload which occurs as a result of such a transition will cause the EXF2 (T2CON.6) flag to be set, triggering a Timer 2 interrupt if said interrupt has been enabled.

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