Motorola DSP96002 - Manual (Page 122)

7 - 36 DSP96002 USER’S MANUAL MOTOROLA
A data read transfer is initiated when the slave’s
—
H
–
R signal is asserted, indicating that its HI RX register
is full and the data is ready to be read by the external DMA Controller.
—
H
–
R is connected to a
—
R
—
E
–
Q
pin in the master which is a DMA service request input. When
—
H
–
R is asserted, the external DMA Con-
troller transfers the data word from the RX register in the slave’s HI to a memory location. The RX register
is read by asserting
—
H
–
A and TREQ=0 and RREQ=1. After RX is read (negating
—
H
–
R), the HI may
transfer the next data word from the HI HTX register, setting HTDE and RXDF. Setting RXDF causes
—
H
–
R to be asserted since RREQ is set. In the slave’s on-chip DMA Controller, HTDE is defined as a DMA ser-
vice request signal. When HTDE is asserted, the slave’s on-chip DMA Controller initiates a data transfer
from the slave memory to the HTX register, keeping the register full for further data transfers.
7.4.21 HI Performance Analysis and Programming Examples
The following host programming examples show the software needed to support Master-Slave transfers be-
tween two DSP96002s. Master processor load, the minimal transfer cycle, and the overhead are estimated.
These estimates can vary depending on the addressing mode. In most cases the fastest addressing mode
possible was used. Also, it was assumed that the master processor did not loose the bus in the middle of
host activity. The HI registers are accessed by the host processor with 0 wait states.
External DMA Controller
Bus Master DSP96002
Bus Slave
DMA Request
Bus Master
Read Bus Cycle
into Memory
—
R
—
E
–
Q
data
full —
H
–
R
—
H
–
A
D0–D31
DMA Request
Memory
→
Host
DMA Transfer
Host Data Empty
—
A
—
C
–
K
Figure 7-20. DSP96002 to External DMA Data Read
(HTDE=1)
Receive Data Full
(RXDF=1)