MC68HC711D3_05 Datasheet, PDF (48/138 Pages) Freescale Semiconductor, Inc – Microcontrollers

Resets, Interrupts, and Low-Power Modes
The sequence for resetting the watchdog timer is:
1. Write $55 to the COP reset register (COPRST) to arm the COP timer clearing mechanism.
2. Write $AA to the COPRST register to clear the COP timer
Both writes must occur in this sequence prior to the timeout, but any number of instructions can be
executed between the two writes.
Table 4-1. COP Time Out Periods
E ÷ 2¹⁵
CR0 CR1 _Divided
By
XTAL = 2²³
Time Out
–0/+15.6 ms
XTAL =
8.0 MHz
Time Out
–0/+16.4 ms
XTAL =
4.9152 MHz
Time Out
–0/+26.7 ms
XTAL =
4.0 MHz
Time Out
–0/+32.8 ms
XTAL =
3.6864 MHz
Time Out
–0/+35.6 ms
00
1
15.625 ms 16.384 ms 26.667 ms 32.768 ms 35.556 ms
01
4
62.5 ms
65.536 ms 106.67 ms 131.07 ms 142.22 ms
10
16
250 ms
262.14 ms 426.67 ms 524.29 ms 568.89 ms
11
64
1 sec
1.049 sec 1.707 sec
2.1 sec
2.276 ms
E=
2.1 MHz
2.0 MHz 1.2288 MHz 1.0 MHz
921.6 kHz
Address: $003A
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Write:
Reset: 0
0
0
0
0
0
0
0
Figure 4-1. Arm/Reset COP Timer Circuitry Register (COPRST)
4.2.4 Clock Monitor Reset
The MCU contains a clock monitor circuit that measures the E-clock frequency. If the E-clock input rate
is above approximately 200 kHz, then the clock monitor does not generate an MCU reset. If the E-clock
signal is lost or its frequency falls below 10 kHz, then an MCU reset can be generated, and the RESET
pin is driven low to reset the external system.
4.2.5 System Configuration Options Register
The system configuration options register (OPTION) is a special-purpose register with several
time-protected bits. OPTION is used during initialization to configure internal system options.
Bits 5, 4, 2, 1, and 0 can be written only once during the first 64 E-clock cycles after reset in normal modes
(where the HPRIO register bit (SMOD) is cleared). In special modes (where SMOD = 1), the bits can be
written at any time. Bit 3 can be written at anytime.
MC68HC711D3 Data Sheet, Rev. 2.1
48
Freescale Semiconductor