Stereo System User Manual

Parallel Host Interface
Host Interface (HI)
MOTOROLA DSP56012 User’s Manual 4-41
4.4.7.5 Servicing DMA Interrupts
When HM0 ≠ 0 and/or HM1 ≠ 0, HOREQ will be asserted to request a DMA
transfer. Generally the HOREQ
pin will be connected to the REQ input of a DMA
controller. The HOA[2:0], HR/W
, and HEN pins are not used during DMA transfers;
DMA transfers only use the HOREQ
and HACK pins after the DMA channel has
been initialized. HACK
is used to strobe the data transfer, as shown in Figure 4-17
on page 4-41 where an MC68440 is used as the DMA controller. DMA transfers to
and from the HI are presented in more detail in Section 4.4.8 Host Interface
Application Examples.
Figure 4-17 DMA Transfer Logic and Timing
DMA ACK Gated Off
Fast Interrupt
To Transfer 24-bit Word
High
Byte
MC68440
IRQ
ACK0
+5 V
DSP56012
To IRQB
+5 V
+5 V
HOREQ
HACK
REQ0
CI
Q
D
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
8T
A0
A1
AS
OWN
AA0325k