Freescale Semiconductor, Inc.
Internal Bus Monitor
The SIM40 provides an internal bus monitor to monitor the DSACK≈ response time for
all internal bus accesses. An option allows the monitoring of external bus accesses. For
external bus accesses, four selectable response times are provided to allow for
variations in response speed of memory and peripherals used in the system. A bus
error signal is asserted internally if the DSACK≈ response limit is exceeded. BERR is
not asserted externally. This monitor can be disabled for external bus cycles only.
Double Bus Fault Monitor
The double bus fault monitor causes a reset to occur if the internal HALT is asserted by
the CPU32, indicating a double bus fault. A double bus fault results when a bus or
address error occurs during the exception processing sequence for a previous bus or
address error, a reset, or while the CPU32 is loading information from a bus error stack
frame during an RTE instruction. This function can be disabled. See Section 3 Bus
Operation for more information.
Spurious Interrupt Monitor
If no interrupt arbitration occurs during an interrupt acknowledge (IACK) cycle, the bus
error signal is asserted internally. This function cannot be disabled.
Software Watchdog
The software watchdog asserts reset or a level 7 interrupt (as selected by the system
protection and control register) if the software fails to service the software watchdog for
a designated period of time (i.e., because it is trapped in a loop or lost). There are eight
selectable timeout periods. This function can be disabled.
Periodic Interrupt Timer
The SIM40 provides a timer to generate periodic interrupts. The periodic interrupt time
period can vary from 122 µs to 15.94 s (with a 32.768-kHz crystal used to generate the
system clock). This function can be disabled.
Figure 4-2 shows a block diagram of the system configuration and protection function.
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MC68340 USER’S MANUAL
MOTOROLA
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