MC68HC705 MOTOROLA [Motorola, Inc], MC68HC705 Datasheet - Page 60

• Manufacturer Part Number: MC68HC705
• Description: HCMOS Microcontroller Unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Resets
5.3.1 Power-On Reset (POR)
5.3.2 External Reset
5.3.3 Programmable and Non-Programmable COP Watchdog Resets
Technical Data
60
A positive transition on the V
The POR is strictly for the power-up condition and cannot be used to
detect drops in power supply voltage.
A 4064 t
active allows the clock generator to stabilize. If the RESET pin is at
logic 0 at the end of 4064 t
until the signal on the RESET pin goes to logic 1.
The minimum time required for the MCU to recognize a reset is 1 1/2
t
as an external reset and not as a COP or clock monitor reset, the RESET
pin must be low for eight t
is sampled. If the pin is still low, an external reset has occurred. If the
input is high, then the MCU assumes that the reset was initiated
internally by either the COP watchdog timer or by the clock monitor. This
method of differentiating between external and internal reset conditions
assumes that the RESET pin will rise to a logic 1 less than two t
its release and that an externally generated reset should stay active for
at least eight t
A timeout of a COP watchdog generates a COP reset. A COP watchdog,
once enabled, is part of a software error detection system and must be
cleared periodically to start a new timeout period.
The MC68HC705C8A has two different COP watchdogs for
compatibility with devices such as the MC68HC705C8 and the
MC68HC05C4A:
CYC
1. Programmable COP watchdog reset
2. Non-programmable COP watchdog
. However, to guarantee that the MCU recognizes an external reset
CYC
(internal clock cycle) delay after the oscillator becomes
CYC
.
Resets
CYC
CYC
DD
. After six t
, the MCU remains in the reset condition
pin generates a power-on reset (POR).
CYC
, the input on the RESET pin
MC68HC705C8A — Rev. 2.0
MOTOROLA
CYC
after