SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 98

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

On-Chip Peripheral Components
Reload of Timer 2
The reload mode for timer 2 is selected by bits T2R0 and T2R1 in SFR T2CON as listed in figure
7-34 b). Two reload modes are selectable:
In mode 0, when timer 2 rolls over from all 1’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 0000 H .
In mode 1, 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.
Figure 7-34 b)
Timer 2 in Reload Mode
Semiconductor Group
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