Retry Operation; Late Bus Error With Dsack - Motorola MC68340 User Manual

CLKOUT
A31–A0
FC3–FC0
R/W
AS
DS
DSACKx
D15–D0
BERR

3.5.2 Retry Operation

When both BERR and HALT are asserted by an external device during a bus cycle, the
MC68340 enters the retry sequence shown in Figure 3-19. A delayed retry, which is
similar to the delayed BERR signal described previously, can also occur (see Figure 3-20).
The MC68340 terminates the bus cycle, places the control signals in their inactive state,
and does not begin another bus cycle until the BERR and HALT signals are negated by
external logic. After a synchronization delay, the MC68340 retries the previous cycle using
the same access information (address, function code, size, etc.). BERR should be negated
before S2 of the retried cycle to ensure correct operation of the retried cycle.
3-36
Freescale Semiconductor, Inc.
S0 S2 S4
WRITE
CYCLE PROCESSING
Figure 3-18. Late Bus Error with DSACK
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S0 S2
INTERNAL STACK
WRITE
S4
MOTOROLA