MC68HC908JK1 Datasheet, PDF (80/210 Pages) Motorola, Inc – MC68HC908JK1

System Integration Module (SIM)
7.4.2.5 LVI Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when
the V_DD voltage falls to the LVI trip voltage V_TRIP. The LVI bit in the SIM
reset status register (SRSR) is set, and the external reset pin (RSTB) is
held low while the SIM counter counts out 4096 2OSCCLK cycles. Sixty-
four 2OSCOUT cycles later, the CPU and memories are released from
reset to allow the reset vector sequence to occur. The SIM actively pulls
down the (RSTB) pin for all internal reset sources.
7.5 SIM Counter
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 uses 12 stages for counting, followed by a 13th stage that
triggers a reset of SIM counters and supplies the clock for the COP
module. The SIM counter is clocked by the falling edge of 2OSCOUT.
7.5.1 SIM Counter During Power-On Reset
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.
7.5.2 SIM Counter During Stop Mode Recovery
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 mask
option register. If the SSREC bit is a logic one, then the stop recovery is
reduced from the normal delay of 4096 2OSCOUT cycles down to 32
2OSCOUT 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 in the configuration register (CONFIG).
Technical Data
80
System Integration Module (SIM)
MC68H(R)C908JL3 — Rev. 1.0
MOTOROLA