MC68336/376
SYSTEM INTEGRATION MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
5-14
The monitor does not check DSACK response on the external bus unless the CPU32
initiates a bus cycle. The BME bit in SYPCR enables the internal bus monitor for inter-
nal to external bus cycles. If a system contains external bus masters, an external bus
monitor must be implemented and the internal-to-external bus monitor option must be
disabled.
When monitoring transfers to an 8-bit port, the bus monitor does not reset until both
byte accesses of a word transfer are completed. Monitor time-out period must be at
least twice the number of clocks that a single byte access requires.
5.4.3 Halt Monitor
The halt monitor responds to an assertion of the HALT signal on the internal bus,
caused by a double bus fault. A flag in the reset status register (RSR) indicates that
the last reset was caused by the halt monitor. Halt monitor reset can be inhibited by
more information.
5.4.4 Spurious Interrupt Monitor
During interrupt exception processing, the CPU32 normally acknowledges an interrupt
request, recognizes the highest priority source, and then either acquires a vector or
responds to a request for autovectoring. The spurious interrupt monitor asserts the
internal bus error signal (BERR) if no interrupt arbitration occurs during interrupt
exception processing. The assertion of BERR causes the CPU32 to load the spurious
interrupt exception vector into the program counter. The spurious interrupt monitor
cannot be disabled. Refer to 5.8 Interrupts for more information. For detailed infor-
5.4.5 Software Watchdog
The software watchdog is controlled by the software watchdog enable (SWE) bit in
SYPCR. When enabled, the watchdog requires that a service sequence be written to
the software service register (SWSR) on a periodic basis. If servicing does not take
place, the watchdog times out and asserts the RESET signal.
Each time the service sequence is written, the software watchdog timer restarts. The
sequence to restart consists of the following steps:
1. Write $55 to SWSR.
2. Write $AA to SWSR.
Both writes must occur before time-out in the order listed. Any number of instructions
can be executed between the two writes.
Watchdog clock rate is affected by the software watchdog prescale (SWP) bit and the
software watchdog timing (SWT[1:0]) field in SYPCR.
SWP determines system clock prescaling for the watchdog timer and determines that
one of two options, either no prescaling or prescaling by a factor of 512, can be