mc68hc908ld64 Freescale Semiconductor, Inc, mc68hc908ld64 Datasheet - Page 122

• Manufacturer Part Number: mc68hc908ld64
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

System Integration Module (SIM)
9.4.2.5 Illegal Address Reset
9.5 SIM Counter
9.5.1 SIM Counter During Power-On Reset
9.5.2 SIM Counter During Stop Mode Recovery
Data Sheet
122
An opcode fetch from an unmapped address generates an illegal
address reset. The SIM verifies that the CPU is fetching an opcode prior
to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not
generate a reset. The SIM actively pulls down the RST pin for all internal
reset sources.
The SIM counter is used by the power-on reset module (POR) and in
stop mode recovery to allow the oscillator time to stabilize before
enabling the internal bus (IBUS) clocks. The SIM counter also serves as
a prescaler for the computer operating properly module (COP). The SIM
counter overflow supplies the clock for the COP module. The SIM
counter is 12 bits long and is clocked by the falling edge of OSCXCLK.
The power-on reset module (POR) detects power applied to the MCU.
At power-on, the POR circuit asserts the signal PORRST. Once the SIM
is initialized, it enables the oscillator to drive the bus clock state machine.
The SIM counter also is used for stop mode recovery. The STOP
instruction clears the SIM counter. After an interrupt, break, or reset, the
SIM senses the state of the short stop recovery bit, SSREC, in the
configure register (CONFIG). If the SSREC bit is a logic one, then the
stop recovery is reduced from the normal delay of 4096 OSCXCLK
cycles down to 32 OSCXCLK cycles. This is ideal for applications using
canned oscillators that do not require long start-up times from stop
mode. External crystal applications should use the full stop recovery
time, that is, with SSREC cleared.
System Integration Module (SIM)
MC68HC908LD64
Freescale Semiconductor
—
Rev. 3.0