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7- 50 M68040 USER’S MANUAL MOTOROLA
require a pullup resistor to maintain a logic-one level between bus master tenures. The
alternate bus master should negate these signals before three-stating to minimize rise
time of the signals and ensure that the processor recognizes the correct level on the next
BCLK rising edge. At the end of C3, the processor recognizes the bus grant and bus idle
conditions (BG asserted and BB negated) and assumes ownership of the bus by asserting
BB and immediately beginning a bus cycle during C4. During C6, the processor begins the
second bus cycle for the misaligned operand and negates BR since no other accesses are
pending. During C7, the external bus arbiter grants the bus back to the alternate bus
master that is waiting for the processor to relinquish the bus. The processor negates BB
and TIP before three-stating these and all other bus signals during C8. Finally, the
alternate bus master recognizes the bus grant and idle conditions at the end of C8 and is
able to resume bus activity during C9.
A31–A0
BCLK
D31–D0
TRANSFER
ATTRIBUTES
TS
TIP
TA
ALTERNATE
MASTER PROCESSOR
BR
BG
BB
AM_BR
AM_BG
ALTERNATE
MASTER
C1 C2 C3 C4 C5 C8 C9C6 C7
*
*
*AM indicates the alternate bus master.
Figure 7-32. Processor Bus Request Timing
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