Motorola M68000 - Halt Operation

MOTOROLA M68000 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL 5- 27
S0
S2
S4
S6
CLK
FC2–FC0
A23–A1
S0
S2
S4
S6
AS
R/W
DTACK
D0–D15
BERR
HALT
UDS
LDS
RETRY
HALT
READ
Figure 5-28. Delayed Retry Bus Cycle Timing Diagram
The processor terminates the bus cycle, then puts the address and data lines in the high-
impedance state. The processor remains in this state until HALT is negated. Then the
processor retries the preceding cycle using the same function codes, address, and data
(for a write operation). BERR should be negated at least one clock cycle before HALT is
negated.
NOTE
To guarantee that the entire read-modify-write cycle runs
correctly and that the write portion of the operation is
performed without negating the address strobe, the processor
does not retry a read-modify-write cycle. When a bus error
occurs during a read-modify-write operation, a bus error
operation is performed whether or not HALT is asserted.
5.4.3 Halt Operation (
HALT)
HALT performs a halt/run/single-step operation similar to the halt operation of an
MC68000. When HALT is asserted by an external device, the processor halts and remains
halted as long as the signal remains asserted, as shown in Figure 5-29.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
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