MC68HC11F1 Datasheet, PDF (57/68 Pages) Motorola, Inc – Technical Summary 8-Bit Microcontroller

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
1 MHz
2 MHz
3 MHz
4 MHz
5 MHz
6 MHz
Any E
PR[1:0] = 00
1 Count
TCNT
Overflow
1.000 µs 65.536 ms
0.500 µs 32.768 ms
0.333 µs 21.845 ms
0.250 µs 16.384 ms
0.200 µs 13.107 ms
0.167 µs 10.923 ms
1/E
2¹⁶/E
PR[1:0] = 01
1 Count
TCNT
Overflow
4.000 µs 262.144 ms
2.000 µs 131.072 ms
1.333 µs 87.381 ms
1.000 µs 65.536 ms
0.800 µs 52.429 ms
0.667 µs 43.691 ms
4/E
2¹⁸/E
PR[1:0] = 10
PR[1:0] = 11
1 Count
TCNT
Overflow
1 Count
TCNT
Overflow
8.000 µs 524.288 ms 16.000 µs 1.049 s
4.000 µs 262.144 ms 8.000 µs 524.288 ms
2.667 µs 174.763 ms 5.333 µs 349.525 ms
2.000 µs 131.072 ms 4.000 µs 262.144 ms
1.600 µs 104.858 ms 3.200 µs 209.715 ms
1.333 µs 87.381 ms 2.667 µs 174.763 ms
8/E
2¹⁹/E
16/E
2²⁰/E
E-Clock
Frequency
1 MHz
2 MHz
3 MHz
4 MHz
5 MHz
6 MHz
Any E
Table 27 Real-Time Interrupt Periods
RTR[1:0] = 00 RTR[1:0] = 01 RTR[1:0] = 10 RTR[1:0] = 11
8.192 ms
4.096 ms
2.731 ms
2.048 ms
1.638 ms
1.366 ms
2¹³/E
16.384 ms
8.192 ms
5.461 ms
4.096 ms
3.277 ms
2.731 ms
2¹⁴/E
32.768 ms
16.384 ms
10.923 ms
8.192 ms
6.554 ms
5.461 ms
2¹⁵/E
65.536 ms
32.768 ms
21.845 ms
16.384 ms
13.107 ms
10.923 ms
2²¹/E
E-Clock
Frequency
1 MHz
2 MHz
3 MHz
4 MHz
5 MHz
6 MHz
Any E
Table 28 COP Watchdog Time-Out Periods
RTR[1:0] = 00 RTR[1:0] = 01 RTR[1:0] = 10 RTR[1:0] = 11
32.768 ms
16.384 ms
10.923 ms
8.192 ms
6.554 ms
5.461 ms
2¹⁵/E
131.072 ms
65.536 ms
43.691 ms
32.768 ms
26.214 ms
21.845 ms
2¹⁷/E
524.288 ms
262.144 ms
174.763 ms
131.072 ms
104.858 ms
87.381 ms
2¹⁹/E
2.097 s
1.049 s
699.051 ms
524.288 ms
419.430 ms
349.525 ms
2²¹/E
MC68HC11F1/FC0
MC68HC11FTS/D
MOTOROLA
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