DSP56362P datasheet(13/152 Pages) FREESCALE

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External Memory Expansion Port (Port A)

DSP56362 Technical Data, Rev. 4

Freescale Semiconductor

2-7

Output

(deasserted)

Bus Request—BR is an active-low output, never tri-stated. BR is asserted

when the DSP requests bus mastership. BR is deasserted when the DSP

no longer needs the bus. BR may be asserted or deasserted independent

of whether the DSP56362 is a bus master or a bus slave. Bus “parking”

allows BR to be deasserted even though the DSP56362 is the bus master.

(See the description of bus “parking” in the BB signal description.) The bus

request hold (BRH) bit in the BCR allows BR to be asserted under software

control even though the DSP does not need the bus. BR is typically sent to

an external bus arbitrator that controls the priority, parking, and tenure of

each master on the same external bus. BR is only affected by DSP requests

for the external bus, never for the internal bus. During hardware reset, BR is

deasserted and the arbitration is reset to the bus slave state.

Input

Ignored Input

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

arbitration circuit when the DSP56362 becomes the next bus master. When

BG is asserted, the DSP56362 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.

The default mode of operation of this signal requires a setup and hold time

referred to CLKOUT. But CLKOUT operation is not guaranteed from

100MHz and up, so the asynchronous bus arbitration must be used for clock

frequencies 100MHz and above. The asynchronous bus arbitration is

enabled by setting the ABE bit in the OMR register.

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).

The default mode of operation of this signal requires a setup and hold time

referred to CLKOUT. But CLKOUT operation is not guaranteed from

100MHz and up, so the asynchronous bus arbitration must be used for clock

frequencies 100MHz and above. The asynchronous bus arbitration is

enabled by setting the ABE bit in the OMR register.

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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