Chapter 14
System Integration Module (SIM)
14.1 Introduction
This section describes the system integration module (SIM), which supports up to 24 external and/or
internal interrupts. Together with the central processor unit (CPU), the SIM controls all microcontroller unit
(MCU) activities. A block diagram of the SIM is shown in
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
– Stop/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
Table 14-1. Signal Name Conventions
Signal Name
BUSCLKX4
BUSCLKX2
Address bus
Data bus
PORRST
IRST
R/W
Description
Buffered clock from the internal, RC or XTAL oscillator circuit.
The BUSCLKX4 frequency divided by two. This signal is again divided by two
in the SIM to generate the internal bus clocks (bus clock = BUSCLKX4 4).
Internal address bus
Internal data bus
Signal from the power-on reset module to the SIM
Internal reset signal
Read/write signal
14.2 RST and IRQ Pins Initialization
RST and IRQ pins come out of reset as PTA3 and PTA2 respectively. RST and IRQ functions can be
activated by programing CONFIG2 accordingly. Refer to
14.3 SIM Bus Clock Control and Generation
The bus clock generator provides system clock signals for the CPU and peripherals on the MCU. The
system clocks are generated from an incoming clock, BUSCLKX2, as shown in
MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 5
Freescale Semiconductor
153
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
