Typewriter User Manual

4- 4 MC68340 USER’S MANUAL MOTOROLA

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.

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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