MC68HC711E20CFN2 Freescale Semiconductor, MC68HC711E20CFN2 Datasheet - Page 81
Manufacturer Part Number
IC MCU 20K 2MHZ OTP 52-PLCC
Specifications of MC68HC711E20CFN2
Number Of I /o
Program Memory Size
20KB (20K x 8)
Program Memory Type
512 x 8
768 x 8
Voltage - Supply (vcc/vdd)
4.5 V ~ 5.5 V
-40°C ~ 85°C
Package / Case
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Complete this 2-step reset sequence to service the COP timer:
Performing instructions between these two steps is possible as long
as both steps are completed in the correct sequence before the timer times out.
5.2.4 Clock Monitor Reset
The clock monitor circuit is based on an internal resistor capacitor (RC) time delay. If no MCU clock edges
are detected within this RC time delay, the clock monitor can optionally generate a system reset. The
clock monitor function is enabled or disabled by the CME control bit in the OPTION register. The presence
of a timeout is determined by the RC delay, which allows the clock monitor to operate without any MCU
Clock monitor is used as a backup for the COP system. Because the COP needs a clock to function, it is
disabled when the clock stops. Therefore, the clock monitor system can detect clock failures not detected
by the COP system.
Semiconductor wafer processing causes variations of the RC timeout values between individual devices.
An E-clock frequency below 10 kHz is detected as a clock monitor error. An E-clock frequency of 200 kHz
or more prevents clock monitor errors. Using the clock monitor function when the E-clock is below 200
kHz is not recommended.
Special considerations are needed when a STOP instruction is executed and the clock monitor is enabled.
Because the STOP function causes the clocks to be halted, the clock monitor function generates a reset
sequence if it is enabled at the time the stop mode was initiated. Before executing a STOP instruction,
clear the CME bit in the OPTION register to 0 to disable the clock monitor. After recovery from STOP, set
the CME bit to logic 1 to enable the clock monitor. Alternatively, executing a STOP instruction with the
CME bit set to logic 1 can be used as a software initiated reset.
1. Write $55 to COPRST to arm the COP timer clearing mechanism.
2. Write $AA to COPRST to clear the COP timer.
Figure 5-1. Arm/Reset COP Timer Circuitry Register (COPRST)
M68HC11E Family Data Sheet, Rev. 5.1