
SECTION 6: RESETS
MOTOROLA
Page 45
MC68HC705V8 Specification Rev. 2.1
SECTION 6
RESETS
The MCU can be reset from six sources: one external input and five internal restart
conditions. The RESET pin is an input with a Schmitt trigger as shown in Figure 6-1. All the
internal peripheral modules will be reset by the internal reset signal (RST). Refer to Figure
6-2 for reset timing detail.
Figure 6-1:
Reset Block Diagram
6.1
EXTERNAL RESET (RESET)
The RESET pin is the only external source of a reset. This pin is connected to a Schmitt
trigger input gate to provide an upper and lower threshold voltage separated by a minimum
amount of hysteresis. This external reset occurs whenever the RESET pin is pulled below
the lower threshold and remains in reset until the RESET pin rises above the upper
threshold. This active low input will generate the RST signal and reset the CPU and
peripherals. Termination of the external RESET input or the internal COP Watchdog reset
are the only reset sources that can alter the operating mode of the MCU.
NOTE:
Activation of the RST signal is generally referred to as reset of the device,
unless otherwise specied.
CPU
LATCH
RESET
COP Watchdog
(COPR)
RST
OSC
Data
Address
PH2
To other
peripherals
S
Low-Voltage
Reset (LVR)
VDD
IRQ/VTST
Mode
Select
To IRQ
logic
LATCH
R
Power-On Reset
(POR)
VDD
Illegal Address
(ILLADDR)
Address
PH2
CLOCKED
ONE-SHOT
(pulse width = 3 x E-clk)
D
Disabled STOP
instruction
STOPEN