
Timing System
Pulse Accumulator
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Timing System
163
PAOVI and PAOVF — Pulse Accumulator Interrupt Enable and Overflow Flag 
The PAOVF status bit is set each time the pulse accumulator count rolls over 
from $FF to $00. To clear this status bit, write a 1 in the corresponding data bit 
position (bit 5) of the TFLG2 register. The PAOVI control bit allows configuring 
the pulse accumulator overflow for polled or interrupt-driven operation and does 
not affect the state of PAOVF. When PAOVI is 0, pulse accumulator overflow 
interrupts are inhibited, and the system operates in a polled mode, which 
requires that PAOVF be polled by user software to determine when an overflow 
has occurred. When the PAOVI control bit is set, a hardware interrupt request 
is generated each time PAOVF is set. Before leaving the interrupt service 
routine, software must clear PAOVF by writing to the TFLG2 register. 
PAII and PAIF — Pulse Accumulator Input Edge Interrupt Enable Bit and Flag 
The PAIF status bit is automatically set each time a selected edge is detected 
at the PA7/PAI/OC1 pin. To clear this status bit, write to the TFLG2 register with 
a 1 in the corresponding data bit position (bit 4). The PAII control bit allows 
configuring the pulse accumulator input edge detect for polled or 
interrupt-driven operation but does not affect setting or clearing the PAIF bit. 
When PAII is 0, pulse accumulator input interrupts are inhibited, and the system 
operates in a polled mode. In this mode, the PAIF bit must be polled by user 
software to determine when an edge has occurred. When the PAII control bit is 
set, a hardware interrupt request is generated each time PAIF is set. Before 
leaving the interrupt service routine, software must clear PAIF by writing to the 
TFLG2 register. 
F
Freescale Semiconductor, Inc.
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