MOTOROLA
MC68HC11F1/FC0
64
MC68HC11FTS/D
13 Pulse Accumulator
The pulse accumulator can be used either to count events or measure the duration of a particular event.
In event counting mode, the pulse accumulator’s 8-bit counter increments each time a specified edge
is detected on the pulse accumulator input pin, PA7. The maximum clocking rate for this mode is the E-
clock divided by two. In gated time accumulation mode, an internal clock increments the 8-bit counter
at a rate of E-clock
÷
64 while the input at PA7 remains at a predetermined logic level.
13.1 Pulse Accumulator Block Diagram
Figure 18 Pulse Accumulator Block Diagram
13.2 Pulse Accumulator Registers
Bits [7:4] in TMSK2 correspond bit for bit with flag bits in TFLG2. Setting any of these bits enables the
corresponding interrupt source.
TMSK2 — Timer Interrupt Mask 2 $x024
Bit 7
6
5
4
3
2
1
Bit 0
TOI
RTII
PAOVI
PAII
0
0
PR1
PR0
RESET:
0
0
0
0
0
0
0
0
PACNT
8-BIT COUNTER
2:1
MUX
PA7/
ENABLE
OVERFLOW
1
INTERRUPT
REQUESTS
INTERNAL
DATA BUS
INPUT BUFFER
&
EDGE DETECTION
PACTL
TFLG2
TMSK2
PAOVI
PAII
PAEN
PAMOD
PEDGE
PAOVF
PAIF
OUTPUT
BUFFER
PAI EDGE
PAEN
E
÷
64 CLOCK
(FROM MAIN TIMER)
PAI/OC1
FROM
MAIN TIMER
OC1
PAEN
2
CLOCK
FROM
STATUS FLAGS
INTERRUPT ENABLES
CONTROL
DDRA