MOTOROLA M68060 USER’S MANUAL 7-51
7.9.3 Double Bus Fault
A double bus fault occurs when an access or address error occurs during the exception pro-
cessing sequence, e.g., the processor attempts to stack several words containing informa-
tion about the state of the machine while processing an access error exception. If a bus error
occurs during the stacking operation, the second error is considered a double bus fault and
the processor is halted.
The MC68060 indicates a double bus fault condition by continuously driving PSTx with an
encoded value of $1C until the processor is reset. Only an external reset operation can
restart a halted processor. The halted processor releases the external bus by negating BR
and forcing all outputs to a high-impedance state.
Figure 7-40. Line Write Retry Bus Cycle Timing
SIGNALED RETRY CYCLE