MC68HC908AP16CFB datasheet(138/440 Pages) MOTOROLA

138 / 440 page

System Integration Module (SIM)

Data Sheet

MC68HC908AP Family — Rev. 2.5

138

MOTOROLA

9.4 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 overflow supplies the clock for the COP module. The SIM

counter is 13 bits long and is clocked by the falling edge of CGMXCLK.

9.4.1 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 clock generation module (CGM) to drive the

bus clock state machine.

9.4.2 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 1, then the stop recovery is

reduced from the normal delay of 4096 CGMXCLK cycles down to 32

CGMXCLK 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.

9.4.3 SIM Counter and Reset States

External reset has no effect on the SIM counter. (See 9.6.2 Stop Mode

for details.) The SIM counter is free-running after all reset states. (See

9.3.2 Active Resets from Internal Sources for counter control and

internal reset recovery sequences.)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MC68HC908AP16CFB Datasheet(PDF) 138 Page - Motorola, Inc