Freescale Semiconductor, Inc.
MODULE
CONFIGURATION
RESET
STATUS
HALT
DOUBLE BUS
RESET
FAULT MONITOR
REQUEST
BUS
MONITOR
BERR
SPURIOUS
INTERRUPT MONITOR
SOFTWARE
RESET
REQUEST or
IRQ7
SOFTWARE
WATCHDOG
CLOCK
9
2
PRESCALER
PERIODIC
INTERRUPT TIMER
IRQ7-IRQ1
Figure 4-2. System Configuration and Protection Function
4.2.2.1 SYSTEM CONFIGURATION. Aspects of the system configuration are controlled
by the MCR and the autovector register (AVR).
The configuration of port B is controlled by the combination of the FIRQ bit in the MCR
and the port B pin assignment register (PPARB). Port B pins can function as dedicated I/O
lines, chip selects, interrupts, or autovector input.
For debug purposes, internal bus accesses can be shown on the external bus. This
function is called show cycles. The SHEN1, SHEN0 bits in the MCR control show cycles.
Bus arbitration can be either enabled or disabled during show cycles.
Arbitration for servicing interrupts is controlled by the value programmed into the interrupt
arbitration (IARB) field of the MCR. Each module that generates interrupts, including the
SIM40, has an IARB field. The value of the IARB field allows arbitration during an IACK
cycle among modules that simultaneously generate the same interrupt level. No two
modules should share the same IARB value. The IARB must contain a value other than $0
for all modules that can generate interrupts; interrupts with IARB = 0 are discarded as
extraneous. The SIM40 arbitrates for both its own interrupts and externally generated
interrupts.
MOTOROLA
MC68340 USER’S MANUAL
4- 5
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