C515A_9708 Datasheet, PDF (81/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515A
Reload of Tirner 2
The reload mode for timer 2 is selected by bits T2R0 and T2R1 in SFR T2CON. Figure 6-14 shows
the configuration of timer 2 in reload mode.
Mode 0 : When timer 2 rolls over from all l’s to all 0’s, it not only sets TF2 but also causes the timer
2 registers to be loaded with the 16-bit value in the CRC register, which is preset by
software. The reload will happen in the same machine cycle in which TF2 is set, thus
overwriting the count value 0000H.
Mode 1 : When a 16-bit reload from the CRC register is caused by a negative transition at the
corresponding input pin T2EX/P1.5. In addition, this transition will set flag EXF2, if bit
EXEN2 in SFR IEN1 is set. lf the timer 2 interrupt is enabled, setting EXF2 will generate
an interrupt. The external input pin T2EX is sampled in every machine cycle. When the
sampling shows a high in one cycle and a low in the next cycle, a transition will be
recognized. The reload of timer 2 registers will then take place in the cycle following the
one in which the transition was detected.
Input
Clock
TL2
TH2
T2EX
P1.5
Mode 1
Reload
Mode 0
CRCL
CRCH
Figure 6-14
Timer 2 in Reload Mode
EXEN2
TF2
EXF2
1 ^{Timer 2}
Interrupt
Request
MCS01903
Semiconductor Group
6-30
1997-08-01