Motorola DSP56012 - Manual (Page 141)

Parallel Host Interface
Host Interface (HI)
MOTOROLA DSP56012 User’s Manual 4-61
4.4.8.3.1 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 4-36 and Figure 4-37
on page 4-63).
1. Host asserts the HOREQ pin when TXDE = 1.
2. DMA controller enables data on H0–H7 and asserts HACK.
3. When HACK is asserted, the host deasserts HOREQ.
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 HOREQ is again asserted. Steps 2–5 are then
repeated.
6. If TXL ($7) was written, TXDE will be cleared 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 HORX (provided that
HRDF = 0). After the transfer to HORX, TXDE will be set, and HOREQ will be
asserted to start the transfer of another word from external memory to the HI.
Figure 4-36 DMA Transfer and HI Interrupts
XFEREQ
XFERACK
DMA
CONTROLLER
HOREQ
HACK
DSP56012
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:$0030 MOVE X:$FFE8, A READ HORX
P:$0031 MOVE A, Y:(R7)+; AND PUT INTO Y MEMORY
AA0342.11