HOST INTERFACE (HI)
5 - 38
PORT B
MOTOROLA
5.3.5.5
Servicing DMA Interrupts
When HM0
≠
0 and/or HM1
≠
0, HREQ will be asserted to request a DMA transfer. Gener-
ally the HREQ pin will be connected to the REQ input of a DMA controller. The HA0-2,
HEN, and HR/W pins are not used during DMA transfers; DMA transfers only use the
HREQ and HACK pins after the DMA channel has been initialized. HACK is used to strobe
the data transfer as shown in Figure 5-18 where an MC68440 is used as the DMA con-
troller. DMA transfers to and from the HI are considered in more detail in Section 5.3.6 HI
Application Examples.
5.3.6
HI Application Examples
The following paragraphs describe examples of initializing the HI, transferring data with
the HI, bootstrapping via the HI, and performing DMA transfers through the HI.
5.3.6.1
HI Initialization
Initializing the HI takes two steps (see Figure 5-19). The first step is to initialize the DSP
DMA ACK GATED OFF
FAST INTERRUPT
TO TRANSFER 24-BIT WORD
HIGH
BYTE
MC68440
IRQ
ACK0
+5 V
DSP56002
TO IRQB
+5 V
+5 V
HREQ
HACK
REQ0
CI
Q
D
A0
A1
AS
OWN
BURST
REQ0
HACK
HIGH
BYTE
MIDDLE
BYTE
LOW
BYTE
1 DMA CYCLE = 8T = 4 DMA CLOCK CYCLES
MAX. MC68440 CLOCK = 10 MHz = > T = 50 ns
Figure 5-18 DMA Transfer Logic and Timing
8T
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..