MC68306 Motorola, MC68306 Datasheet - Page 45

• Manufacturer Part Number: MC68306
• Description: Integrated EC000 Processor
• Manufacturer: Motorola

There are two ways to arbitrate the bus, 3-wire and 2-wire bus arbitration. The EC000
core can do either 2-wire or 3-wire bus arbitration. Figures 3-12 and 3-14 show 3-wire bus
arbitration and Figures 3-13 and 5-15 show 2-wire bus arbitration. BGACK must be pulled
high for 2-wire bus arbitration.
MOTOROLA
1) NEGATE BG (AND WAIT FOR BGACK
2) IF BR REMAINS ASSERTED AFTER
1) ASSERT BUS GRANT (BG)
TO BE NEGATED)
BGACK ASSERTED, RE-ASSERT BG.
TERMINATE ARBITRATION
REARBITRATE OR RESUME
GRANT BUS ARBITRATION
PROCESSOR OPERATION
Figure 3-12. Three-Wire Bus Arbitration Cycle Flowchart
PROCESSOR
MC68306 USER'S MANUAL
1) PERFORM DATA TRANSFERS (READ
1) EXTERNAL ARBITRATION DETER-
2) NEXT BUS MASTER WAITS FOR
3) NEXT BUS MASTER ASSERTS BUS
4) BUS MASTER NEGATES BR
1) ASSERT BUS REQUEST (BR)
1) NEGATE BGACK
ACKNOWLEDGE BUS MASTERSHIP
AND WRITE CYCLES) ACCORDING
TO THE SAME RULES THE PRO-
CESSOR USES
MINES NEXT BUS MASTER
CURRENT CYCLE TO COMPLETE
GRANT ACKNOWLEDGE (BGACK)
TO BECOME NEW MASTER
OPERATE AS BUS MASTER
RELEASE BUS MASTERSHIP
REQUESTING DEVICE
REQUEST THE BUS
3- 13