DSP56366P datasheet(11/110 Pages) FREESCALE

11 / 110 page

DSP56366 Technical Data, Rev. 3.1

Freescale Semiconductor

2-7

Input

Ignored Input Bus Grant—BG is an active-low input. BG is asserted by an external bus

arbitration circuit when the DSP56366 becomes the next bus master. When BG

is asserted, the DSP56366 must wait until BB is deasserted before taking bus

mastership. When BG is deasserted, bus mastership is typically given up at the

end of the current bus cycle. This may occur in the middle of an instruction that

requires more than one external bus cycle for execution.

For proper BG operation, the asynchronous bus arbitration enable bit (ABE) in

the OMR register must be set.

Input/Output

Input

Bus Busy—BB is a bidirectional active-low input/output. BB indicates that the

bus is active. Only after BB is deasserted can the pending bus master become

the bus master (and then assert the signal again). The bus master may keep

BB asserted after ceasing bus activity regardless of whether BR is asserted or

deasserted. This is called “bus parking” and allows the current bus master to

reuse the bus without rearbitration until another device requires the bus. The

deassertion of BB is done by an “active pull-up” method (i.e., BB is driven high

and then released and held high by an external pull-up resistor).

For proper BB operation, the asynchronous bus arbitration enable bit (ABE) in

the OMR register must be set.

BB requires an external pull-up resistor.

Table 2-7 External Bus Control Signals (continued)

Signal Name

Type

State during

Reset

Signal Description

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