MC68HC11F1/FC0
MOTOROLA
MC68HC11FTS/D
57
12 Main Timer
The main timer is based on a free-running 16-bit counter with a four-stage programmable prescaler. The
timer drives the three input capture (IC) channels, four output compare (OC) channels, one channel pro-
grammable for either IC or OC, and the pulse accumulator (PA). All of these functions share port A. The
main timer also drives the pulse accumulator, real-time interrupt (RTI), and computer operating properly
(COP) watchdog circuits.
12.1 Timer Operation
The following tables summarize timing periods for various M68HC11 functions derived from the main
timer for several crystal frequencies.
Table 26 Timer Subsystem Count and Overflow Periods
E-Clock
Frequency
PR[1:0] = 00
PR[1:0] = 01
PR[1:0] = 10
PR[1:0] = 11
1 Count
TCNT
Overflow
1 Count
TCNT
Overflow
1 Count
TCNT
Overflow
1 Count
TCNT
Overflow
1 MHz
1.000
µ
s
65.536 ms
4.000
µ
s
262.144 ms
8.000
µ
s
524.288 ms 16.000
µ
s
1.049 s
2 MHz
0.500
µ
s
32.768 ms
2.000
µ
s
131.072 ms
4.000
µ
s
262.144 ms
8.000
µ
s
524.288 ms
3 MHz
0.333
µ
s
21.845 ms
1.333
µ
s
87.381 ms
2.667
µ
s
174.763 ms
5.333
µ
s
349.525 ms
4 MHz
0.250
µ
s
16.384 ms
1.000
µ
s
65.536 ms
2.000
µ
s
131.072 ms
4.000
µ
s
262.144 ms
5 MHz
0.200
µ
s
13.107 ms
0.800
µ
s
52.429 ms
1.600
µ
s
104.858 ms
3.200
µ
s
209.715 ms
6 MHz
0.167
µ
s
10.923 ms
0.667
µ
s
43.691 ms
1.333
µ
s
87.381 ms
2.667
µ
s
174.763 ms
Any E
1/E
2
16
/E
4/E
2
18
/E
8/E
2
19
/E
16/E
2
20
/E
Table 27 Real-Time Interrupt Periods
E-Clock
Frequency
RTR[1:0] = 00
RTR[1:0] = 01
RTR[1:0] = 10
RTR[1:0] = 11
1 MHz
8.192 ms
16.384 ms
32.768 ms
65.536 ms
2 MHz
4.096 ms
8.192 ms
16.384 ms
32.768 ms
3 MHz
2.731 ms
5.461 ms
10.923 ms
21.845 ms
4 MHz
2.048 ms
4.096 ms
8.192 ms
16.384 ms
5 MHz
1.638 ms
3.277 ms
6.554 ms
13.107 ms
6 MHz
1.366 ms
2.731 ms
5.461 ms
10.923 ms
Any E
2
13
/E
2
14
/E
2
15
/E
2
21
/E
Table 28 COP Watchdog Time-Out Periods
E-Clock
Frequency
RTR[1:0] = 00
RTR[1:0] = 01
RTR[1:0] = 10
RTR[1:0] = 11
1 MHz
32.768 ms
131.072 ms
524.288 ms
2.097 s
2 MHz
16.384 ms
65.536 ms
262.144 ms
1.049 s
3 MHz
10.923 ms
43.691 ms
174.763 ms
699.051 ms
4 MHz
8.192 ms
32.768 ms
131.072 ms
524.288 ms
5 MHz
6.554 ms
26.214 ms
104.858 ms
419.430 ms
6 MHz
5.461 ms
21.845 ms
87.381 ms
349.525 ms
Any E
2
15
/E
2
17
/E
2
19
/E
2
21
/E
Содержание Semiconductor MC68HC11F1
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