Motorola DSP56301 - Manual (Page 114)

General-Purpose Input/Output (GPIO)
5 -4 DSP56301 User’s Manual
5.3.3 DMA
The Direct Memory Access (DMA) controller permits data transfers between internal/
external memory and/or internal/external I/O in any combination without the intervention of
the core. Dedicated DMA address and data buses and internal memory partitioning ensure
achievement of high-level isolation so the DMA operation does not interfere with or slow
down core operation. The DMA moves data to/from the peripheral transmit/receive registers.
You can use the DMA control registers to configure sources and destinations of data transfers.
Depending on the peripheral, one to four peripheral request sources are available. This is the
most efficient method of data transfer available. Core intervention is not required after the
DMA channel is initialized. DMA requires more initialization code and consideration of
DMA modes. However, it is the most efficient use of core resources. Once these registers are
programmed, you must enable the DMA by triggering a DMA request off one of the
peripheral control flags or enabling it in normal program flow or an interrupt service routine.
5.3.4 Advantages and Disadvantages
Polling is the easiest method to implement, but it requires a large amount of DSP56300 core
processing power. The core cannot be involved in other processing activities while it is
polling receive and transmit ready bits. Interrupts require more code, but the core can process
other routines while waiting for data I/O. An interrupt is generated when data is ready to be
transferred to or from the peripheral device. DMA requires even less core intervention, and
the setup code is minimal, but the DMA channels must be available.
5.4 General-Purpose Input/Output (GPIO)
The DSP56301 provides 42 bidirectional pins that can be configured as GPIO signals or as
peripheral-dedicated signals or some combination of both depending on the peripheral. No
dedicated GPIO pins are provided. All peripheral pins, except those of the HI32, are GPIO
inputs by default after reset. The control register settings of the DSP56301 peripherals
determine whether these pins function as GPIO or as peripheral-dedicated signals or some
combination of both. This section tells how signals are used as GPIO. Chapter 2,
Signals/Connections details the special uses of the 42 bidirectional pins. These signals fall
into five groups and are controlled separately or as a group:
n Port B—24 GPIO signals (shared with part of the host interface signals)
n Port C—6 GPIO signals (shared with the ESSI0 signals)
n Port D—6 GPIO signals (shared with the ESSI1 signals)
n Port E—3 GPIO signals (shared with the SCI signals)
n Timers—3 GPIO signals (shared with the triple timer signals)