Datasheet

Bus Operation

MOTOROLA MCF5206e USER’S MANUAL 6-65

master of the external bus. Also during C4, the external arbiter removes the grant from the

MCF5206e by negating bus grant (BG). Because the MCF5206e is the current bus master

and the bus lock bit in the SIMR is set to 1, it continues to assert BD even after the current

transfer has completed. The MCF5206e negates the bus lock bit in the SIMR during C8.

Because bus grant (BG) is negated, the MCF5206e negates bus driven (BD) during C9

and three-states the external bus, thereby passing ownership of the external bus to an

external master.

BR can be used by the external arbiter as an indication that the MCF5206e needs the bus.

However, there is no guarantee that when the bus is granted to the MCF5206e, a bus

cycle is performed. At best, BR must be used as a status output that indicates when the

MCF5206e needs the bus, but not as an indication that the MCF5206e is in a certain bus

arbitration state.

Figure 6-40, a high level bus arbitration state diagram for the MCF5206e bus arbitration

protocol, can be used by external arbiters to predict how the MCF5206e operates as a

function of external signals. Table 6-11 lists conditions that cause a change to and from

the various states. Table 6-12 describes the MCF5206e bus ownership, bus driving, and

assertion of bus driven (BD) for each state of the bus arbitration state machine.

Figure 6-40. MCF5206e Bus Arbitration Protocol State Diagram

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