MC68HC11EA9 Datasheet, PDF (31/58 Pages) Motorola, Inc – 8 BIT HCMOS SINGLE CHIP MICROCONTOROLLER WITH A/D CONVERTER

Freescale Semiconductor, Inc.
7 Timing System
The timing system is based on a free-running 16-bit counter with a four-stage programmable prescaler.
A timer overflow function allows software to extend the system’s timing capability beyond the counter's
16-bit range. The main timer consists of the timer prescaler, the 16-bit free-running counter, and the
capture/compare unit. 7.2 Main Timer details this portion of the timing system.
The free-running counter can be driven by either the EXTAL signal, as in other M68HC11 derivatives
or it can be driven by a software-controlled phase-locked loop (PLL) frequency synthesizer which has
been added to the MC68HC(7)11EA9 MCUs. The PLL allows the MCU to operate in WAIT mode with
extremely low power requirements. Refer to 7.1 Phase-Locked Loop Synthesizer.
In addition, the timing system includes pulse accumulator and real-time interrupt (RTI) functions, as well
as a clock monitor function, which can be used to detect clock failures that are not detected by the COP
system. Refer to the appropriate paragraphs within this section for information regarding these func-
tions. Table 12 shows a summary of the crystal-related frequencies and periods.
Control Bits
PR[1:0]
00
1 count —
overflow —
01
1 count —
overflow —
10
1 count —
overflow —
11
1 count —
overflow —
RTR[1:0]
00
01
10
11
CR[1:0]
00
01
10
11
Time-out Tolerance
(–0 ms/+...)
Table 12 Timer Summary
Common System Frequencies
4.0 MHz
8.0 MHz
12.0 MHz
1.0 MHz
2.0 MHz
3.0 MHz
Main Timer Count Rate (Period Length)
1000 ns
65.536 ms
500 ns
32.768 ms
333 ns
21.845 ms
4.0 µs
262.14 ms
2.0 µs
131.07 ms
1.333 µs
32.768 ms
8.0 µs
524.28 ms
4.0 µs
262.14 ms
2.667 µs
174.76 ms
16.0 µs
8.0 µs
5.333 µs
1.049 s
524.29 ms
349.52 ms
Periodic (RTI) Interrupt Rates (Period Length)
8.192 ms
4.096 ms
2.731 ms
16.384 ms
8.192 ms
5.461 ms
32.768 ms
16.384 ms
10.923 ms
65.536 ms
32.768 ms
21.845 ms
COP Watchdog Timeout Rates (Period Length)
32.768 ms
16.384 ms
10.923 ms
131.072 ms
65.536 ms
43.691 ms
524.288 ms
262.14 ms
174.76 ms
2.098 s
1.049 s
699.05 ms
32.8 ms
16.4 ms
10.9 ms
Definition
XTAL
E
1/E
2¹⁶/E
4/E
2¹⁸/E
8/E
2¹⁹/E
16/E
2²⁰/E
2¹³/E
2¹⁴/E
2¹⁵/E
2¹⁶/E
2¹⁵/E
2¹⁷/E
2¹⁹/E
2²¹/E
2¹⁵/E
MC68HC11EA9
MC68HC11EA9TS/D
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