M68ICS08GR datasheet(281/408 Pages) FREESCALE

281 / 408 page

System Integration Module (SIM)

SIM Counter

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

System Integration Module (SIM)

281

19.4.2.6 Monitor Mode Entry Module Reset (MODRST)

The monitor mode entry module reset (MODRST) asserts its output to

the SIM when monitor mode is entered in the condition where the reset

vectors are blank ($00). (See Entering Monitor Mode.) When MODRST

gets asserted, an internal reset occurs. The SIM actively pulls down the

RST pin for all internal reset sources.

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

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

19.5.1 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 clock generation module (CGM) to drive the

bus clock state machine.

19.5.2 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 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 startup times from stop mode. External crystal

applications should use the full stop recovery time, that is, with SSREC

cleared.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

M68ICS08GR Datasheet(PDF) 281 Page - Freescale Semiconductor, Inc