HOST INTERFACE (HI)
5 - 56
PORT B
MOTOROLA
DSP addressing modes and modifiers. Queues and circular sample buffers are easily cre-
ated for DMA transfer regions. The host exceptions can be programmed as high priority
fast or long exception service routines. The external DMA controller provides the transfers
between the DSP HI registers and the external DMA memory. The external DMA control-
ler must provide the address to the external DMA memory; however, the address of the
selected HI register is provided by a DMA address counter in the HI.
DMA transfers can only be in one direction at a time; however, the host processor can
access any of the registers not in use during the DMA transfer by deasserting HACK and
using HEN and HA0-HA2 to transfer data. The host can therefore transfer data in the other
direction during the DMA operation using polling techniques.
+5 V
DMA
CONTROLLER
TRANSFER REQUEST
TRANSFER
ACKNOWLEDGE
DSP56002
HOST INTERFACE
HREQ
HACK
INTERNAL
ADDRESS
COUNTER
H0 - H7
1K
MEMORY
R/W
CONTROL
ADDRESS
DATA
Characteristics of Host DMA Mode
• The HREQ pin is NOT available for host processor interrupts.
• TREQ and RREQ select the direction of DMA transfer.
— DMA to DSP56002
— DSP56002 to DMA
— Simultaneous bidirectional DMA transfers are not permitted.
• Host processor software polled transfers are permitted in the opposite direction of the DMA transfer.
• 8-, 16-, or 24-bit transfers are supported.
• 16-, or 24-bit transfers reduce the DSP interrupt rate by a factor of 2 or 3, respectively.
Figure 5-36 HI Hardware–DMA Mode
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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