DSP56004ROM datasheet(14/82 Pages) FREESCALE

14 / 82 page

1-8

DSP56004/D, Rev. 3

MOTOROLA

Signal/Connection Descriptions

Interrupt and Mode Control

MODB

IRQB

Input

Input (MODB) Mode Select B—This input signal has two functions:

•

to work with the MODA and MODC signals to select

the DSP’s initial operating mode, and

•

to allow an external device to request a DSP

interrupt after internal synchronization.

MODB is read and internally latched in the DSP when the

processor exits the Reset state. The logic state present on the

MODA, MODB, and MODC pins selects the initial DSP

operating mode. Several clock cycles after leaving the Reset

state, the MODB signal changes to the external interrupt

request IRQB. The DSP operating mode can be changed by

software after reset.

External Interrupt Request B (IRQB

)—The IRQB input is a

synchronized external interrupt request. It may be

programmed to be level-sensitive or negative-edge-

triggered. When the signal is edge-triggered, triggering

occurs at a voltage level and is not directly related to the fall

time of the interrupt signal. However, as the fall time of the

interrupt signal increases, the probability that noise on IRQB

will generate multiple interrupts also increases. Hardware

reset causes this input to function as MODB.

Table 1-7

Interrupt and Mode Control Signals (Continued)

Signal Name

Signal

Type

State during

Reset

Signal Description

Freescale Semiconductor, Inc.

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