MC68030 Datasheet, PDF (234/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Bus Operation
S0
S2
Sw
Sw
Sw
Sw S3
CLK
A31-A0
S0
S2
FC2-FC0
SIZ1–SIZ0
R/W
ECS
OCS
AS
DS
STERM
DBEN
D31-D0
BERR
HALT
WRITE WITH BUS ERROR ASSERTED
INTERNAL
PROCESSING
STACK WRITE
Figure 7-51. Late Bus Error with STERM — Exception Taken
When a bus error occurs after the burst mode has been entered (that is, on the second
access or later), the processor terminates the burst operation, and the cache entry
corresponding to that cycle is marked invalid, but the processor does not take an exception
(see Figure 7-52). If the second cycle is for a portion of a misaligned operand fetch, the
processor runs another read cycle for the second portion with CBREQ negated, as shown
in Figure 7-53. If BERR is asserted again, the MC68030 then takes an exception. The
MC68030 supports late bus errors during a burst fill operation; the timing is the same relative
to STERM and the clock as for a late bus error in a normal synchronous cycle.
7-88
MC68030 USER’S MANUAL
MOTOROLA