mc68hc908gt8 Freescale Semiconductor, Inc, mc68hc908gt8 Datasheet - Page 183

• Manufacturer Part Number: mc68hc908gt8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

15.3.2 Active Resets from Internal Sources
All internal reset sources actively pull the RST pin low for 32 CGMXCLK cycles to allow resetting of
external peripherals. The internal reset signal IRST continues to be asserted for an additional 32 cycles.
See
or POR. See
The COP reset is asynchronous to the bus clock.
The active reset feature allows the part to issue a reset to peripherals and other chips within a system
built around the MCU.
15.3.2.1 Power-On Reset
When power is first applied to the MCU, the power-on reset module (POR) generates a pulse to indicate
that power-on has occurred. The external reset pin (RST) is held low while the SIM counter counts out
4096 + 32 CGMXCLK cycles. Thirty-two CGMXCLK cycles later, the CPU and memories are released
from reset to allow the reset vector sequence to occur.
Freescale Semiconductor
Figure
15-5. An internal reset can be caused by an illegal address, illegal opcode, COP timeout, LVI,
Figure
For LVI or POR resets, the SIM cycles through 4096 CGMXCLK cycles
during which the SIM forces the RST pin low. The internal reset signal then
follows the sequence from the falling edge of RST shown in
CGMXCLK
IRST
RST
IAB
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
15-6.
Reset Recovery Type
All others
POR/LVI
Figure 15-6. Sources of Internal Reset
ILLEGAL ADDRESS RST
ILLEGAL OPCODE RST
Figure 15-5. Internal Reset Timing
RST PULLED LOW BY MCU
Table 15-2. PIN Bit Set Timing
MODRST
32 CYCLES
COPRST
POR
LVI
NOTE
Actual Number of Cycles
4163 (4096 + 64 + 3)
INTERNAL RESET
32 CYCLES
67 (64 + 3)
Figure
VECTOR HIGH
Reset and System Initialization
15-5.
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