MPC8280 datasheet(270/1386 Pages) FREESCALE

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MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

7-12

Freescale Semiconductor

tenure about to be granted (that is, not for another address tenure available because

of address pipelining).

Negated—Indicates that an external device is not granted mastership of the data

bus.

Timing Comments

Assertion—Occurs on the first clock in which the data bus is not busy and the

processor has the highest priority outstanding data transaction.

Negation—Occurs one clock after assertion.

7.2.6.2

Data Bus Busy (DBB)

The data bus busy (DBB) signal is both an input and output signal on the MPC8280.

7.2.6.2.1

Data Bus Busy (DBB)—Output

Following are the state meaning and timing comments for the DBB output signal.

State Meaning

Asserted—Indicates that the MPC8280 is the data bus master. The MPC8280

always assumes data bus mastership if it needs the data bus and determines a

qualified data bus grant (see DBG).

Negated—Indicates that the MPC8280 is not using the data bus.

Timing Comments

Assertion—Occurs during the bus clock cycle following a qualified DBG.

Negation—Occurs for a minimum of one-half bus clock cycle following the

assertion of the final TA following TEA or certain ARTRY cases.

High Impedance—Occurs after DBB is negated.

7.2.6.2.2

Data Bus Busy (DBB)—Input

Following are the state meaning and timing comments for the DBB input signal.

State Meaning

Asserted—Indicates that another device is bus master.

Negated—Indicates that the data bus is free (with proper qualification, see DBG)

for use by the MPC8280.

Timing Comments

Assertion—Must occur when the MPC8280 must be prevented from using the

data bus.

Negation—May occur whenever the data bus is available.

7.2.7

Data Transfer Signals

Data transfer signals are used in the same way in both internal only and external master modes. Like the

address transfer signals, the data transfer signals are used to transmit data and to generate and monitor

parity for the data transfer. For a detailed description of how data transfer signals interact, see

Section 7.2.7, “Data Transfer Signals.”

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