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DSP56300 Datasheet(PDF) 10 Page - Freescale Semiconductor, Inc |
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DSP56300 Datasheet(HTML) 10 Page - Freescale Semiconductor, Inc |
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10 / 100 page  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. BR Output 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. BG 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. BB 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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