Interrupt And Mode Control (3 Pins) - Motorola DSP56156 Manual

leases bus mastership. BB becomes an input when the DSP is no longer the
bus master.
2.4

INTERRUPT AND MODE CONTROL (3 PINS)

MODA/IRQA ( Mode Select A/External Interrupt Request A) - This input has two
functions - to select the initial chip operating mode and, after synchronization,
to allow an external device to request a DSP interrupt. MODA is read and inter-
nally latched in the DSP when the processor exits the reset state. MODA and
MODB select the initial chip operating mode. Several clock cycles after leaving
the reset state, the MODA pin changes to the external interrupt request IRQA.
The chip operating mode can be changed by software after reset. The IRQA in-
put is a synchronized external interrupt request which indicates that an external
device is requesting service. It may be programmed to be level sensitive or neg-
ative edge triggered. If level sensitive triggering is selected, an external pull up
resistor is required for wired-OR operation. If the processor is in the stop stand-
by state and IRQA is asserted, the processor will exit the stop state.
MODB/IRQB (Mode Select B/External Interrupt Request B) - This input has two
functions - to select the initial chip operating mode and, after internal synchro-
nization, to allow an external device to request a DSP interrupt. MODB is read
and internally latched in the DSP when the processor exits the reset state.
MODA and MODB select the initial chip operating mode. Several clock cycles
after leaving the reset state, the MODB pin changes to the external interrupt re-
quest IRQB. After reset, the chip operating mode can be changed by software.
The IRQB input is an external interrupt request which indicates that an external
device is requesting service. It may be programmed to be level sensitive or neg-
ative edge triggered. If level sensitive triggering is selected, an external pull up
resistor is required for wired-OR operation.
MODC (Mode Select C) - This input is used to select the initial bus operating mode.
When tied high, the external bus is programmed in the master mode (BR output
and BG input) and when tied low the bus is programmed in the slave mode (BR
input and BG output). MODC is read and internally latched in the DSP when the
processor exits the reset state. After RESET, the bus operating mode can be
changed by software by writing the MC bit of the OMR register.
RESET (Reset) - This input is a direct hardware reset of the processor. When RESET
is asserted, the DSP is initialized and placed in the reset state. A Schmitt trigger
input is used for noise immunity. When the reset pin is deasserted, the initial
MOTOROLA

INTERRUPT AND MODE CONTROL (3 PINS)

DSP56156 PIN DESCRIPTIONS 2 - 9