
Timing System
Pulse Accumulator
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Timing System
161
Pulse accumulator control bits are also located within two timer registers, TMSK2 
and TFLG2, as described in the following paragraphs. 
9.7.1  Pulse Accumulator Control Register 
Four of this register’s bits control an 8-bit pulse accumulator system. Another bit 
enables either the OC5 function or the IC4 function, while two other bits select the 
rate for the real-time interrupt system.
DDRA7 — Data Direction for Port A Bit 7 
Refer to 
Section 6. Parallel Input/Output (I/O) Ports
. 
PAEN — Pulse Accumulator System Enable Bit
0 = Pulse accumulator disabled 
1 = Pulse accumulator enabled 
PAMOD — Pulse Accumulator Mode Bit
0 = Event counter 
1 = Gated time accumulation 
PEDGE — Pulse Accumulator Edge Control Bit
This bit has different meanings depending on the state of the PAMOD bit, as 
shown in 
Table 9-7
. 
Table 9-6. Pulse Accumulator Timing
Crystal
Frequency
E Clock
Cycle Time
E
 ÷ 
64
PACNT
Overflow 
4.0 MHz
1 MHz
1000 ns
64 
μ
s
16.384 ms 
8.0 MHz
2 MHz
500 ns
32 
μ
s
8.192 ms 
12.0 MHz
3 MHz
333 ns
21.33 
μ
s
5.461 ms 
Address:
$1026
Bit 7
6
5
4
3
2
1
Bit 0
Read:
DDRA7
PAEN
PAMOD
PEDGE
DDRA3
I4/O5
RTR1
RTR0
Write:
Reset:
0
0
0
0
0
0
0
0
Figure 9-25. Pulse Accumulator Control Register (PACTL)
Table 9-7. Pulse Accumulator Edge Control
PAMOD
0
0
1
1
PEDGE
0
1
0
1
Action on Clock 
PAI falling edge increments the counter. 
PAI rising edge increments the counter. 
A 0 on PAI inhibits counting. 
A 1 on PAI inhibits counting. 
F
Freescale Semiconductor, Inc.
For More Information On This Product,
  Go to: www.freescale.com
n
.