Microcontrollers Data Sheet

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 181
Chapter 14
System Integration Module (SIM)
14.1 Introduction
This section describes the system integration module (SIM). Together with the central processor unit
(CPU), the SIM controls all microcontroller unit (MCU) activities.
A block diagram of the SIM is shown in Figure 14-1.
The SIM is a system state controller that coordinates CPU and exception timing. The SIM is responsible
for:
• Bus clock generation and control for CPU and peripherals:
– Wait/reset/break entry and recovery
– Internal clock control
• Master reset control, including power-on reset (POR) and computer operating properly (COP)
timeout
• Interrupt control:
– Acknowledge timing
– Arbitration control timing
– Vector address generation
• CPU enable/disable timing
• Modular architecture expandable to 128 interrupt sources
Table 14-1 shows the internal signal names used in this section.
Table 14-1. Signal Name Conventions
Signal Name Description
CGMXCLK Buffered version of OSC1 from clock generator module (CGM)
CGMVCLK Phase-locked loop (PLL) circuit output
CGMOUT PLL-based or OSC1-based clock output from CGM module (bus clock = CGMOUT divided by two)
IAB Internal address bus
IDB Internal data bus
PORRST Signal from the power-on reset module to the SIM
IRST Internal reset signal
R/W
Read/write signal