HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 57
5.3.6.3.1
Host To DSP Internal Processing
The following procedure outlines the steps that the HI hardware takes to transfer DMA
data from the host data bus to DSP memory (see Figure 5-36 and Figure 5-37).
1. HI asserts the HREQ pin when TXDE=1.
2. DMA controller enables data on H0-H7 and asserts HACK.
3. When HACK is asserted, the HI deasserts HREQ.
4. When the DMA controller deasserts HACK, the data on H0-H7 is latched into
the TXH, TXM, TXL registers.
5. If the byte register written was not TXL (i.e., not $7) the DMA address counter
internal to the HI increments and HREQ is again asserted. Steps 2-5 are then
repeated.
6. If TXL ($7) was written, TXDE will be set to zero and the address counter in
the HI will be loaded with the contents of HM1 and HM0. When TXDE=0, the
contents of TXH:TXM:TXL are transferred to HRX provided HRDF=0. After the
transfer to HRX, TXDE will be set to one, and HREQ will be asserted to start
the transfer of another word from external memory to the HI.
7. When the transfer to HRX occurs within the HI, HRDF is set to one. Assuming
HRIE=1, a host receive exception will be generated. The exception routine
must read the HRX to clear HRDF.
Note:
The transfer of data from the TXH, TXM, TXL registers to the HRX register auto-
XFEREQ
XFERACK
DMA
CONTROLLER
HREQ
HACK
DSP560021
24-BIT TRANSFER
(INTERNAL COUNTER)
16-BIT TRANSFER
(INTERNAL COUNTER)
8-BIT TRANSFER
(INTERNAL COUNTER)
H
(01)
M
(10)
M
(10)
M
(10)
M
(10)
M
(10)
H
(01)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
L
(11)
HOST
RECEIVE
INTERRUPT
FAST INTERRUPT ROUTINE
P:$0020 MOVE X:$FFE8,A
READ HRX
P:$0021 MOVE A, Y:(R7)+
;AND PUT INTO Y MEMORY
Figure 5-37 DMA Transfer and Host Interrupts
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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