DSP56367 datasheet(10/100 Pages) FREESCALE

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Interrupt and Mode Control

DSP56367 Technical Data, Rev. 2.1

2-6

Freescale Semiconductor

2.9

Interrupt and Mode Control

The interrupt and mode control signals select the chip’s operating mode as it comes out of hardware reset.

After RESET is deasserted, these inputs are hardware interrupt request lines.

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 DSP56367 is a

bus master or a bus slave. Bus “parking” allows BR to be deasserted even though the

DSP56367 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 DSP56367 becomes the next bus master. When BG is asserted, the

DSP56367 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

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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