MC68HCP11 Datasheet, PDF (38/45 Pages) Motorola, Inc – 8-Bit Microcontroller

9 Pulse Accumulator
The MC68HC11A8 has an 8-bit counter that can be configured to operate as a simple event counter or
for gated time accumulation, depending on the PAMOD bit in the PACTL register. The pulse accumu-
lator counter can be read or written at any time.
The port A bit 7 I/O pin can be configured as a clock in event counting mode, or as a gate signal to en-
able a free-running clock (E divided by 64) in gated time accumulation mode.
Table 9 Pulse Accumulator Timing
Selected Crystal
CPU Clock
(E)
Cycle Time
(1/E)
Pulse Accumulator (in Gated Mode)
(E/2⁶)
(E/2¹⁴)
1 count —
overflow —
Common XTAL Frequencies
4.0 MHz
8.0 MHz
12.0 MHz
1.0 MHz
2.0 MHz
3.0 MHz
1000 ns
500 ns
333 ns
64.0 µs
16.384 ms
32.0 µs
8.192 ms
21.33 µs
5.461 ms
E ÷ 64 CLOCK
(FROM MAIN TIMER)
PAOVI
PAOVF
PAII
PAIF
1
INTERRUPT
REQUESTS
2
TMSK2 INT ENABLES
MCU PIN
PA7/
PAI/
OC1
INPUT BUFFER
AND
EDGE DETECTOR
OUTPUT
BUFFER
2:1
MUX
DATA
BUS
FROM
MAIN TIMER
OC1
FROM
DDRA7
PACTL CONTROL
TFLG2 INTERRUPT STATUS
PAI EDGE
PAEN
DISABLE
FLAG SETTING
CLOCK
OVERFLOW
PACNT 8-BIT COUNTER
ENABLE
PAEN
INTERNAL
DATA BUS
PULSE ACC BLOCK
Figure 12 Pulse Accumulator System Block Diagram
MOTOROLA
38
MC68HC11A8
MC68HC11A8TS/D